UC-NRLF 


SB    33    DMD 


MOTOR  TRUCK  DESIGN 
AND  CONSTRUCTION 


MOTOR  TRUCK  DESIGN 
AND  CONSTRUCTION 


BY 


C.  T,  SCHAEFER 

CONSULTING   ENGINEER 
MEMBER    SOCIETY    OF    AUTOMOTIVE    ENGINEERS 


292  ILLUSTRATIONS 


NEW  YORK 

D.  VAN  NOSTRAND  COMPANY 

25  PARK  PLACE 

1919 


S3 


COPYRIGHT,  1919,  BY 
D.  VAN  NOSTRAND  COMPANY 


PRESS  OF 

THE  NEW  ERA  PRINTING  COMPANY 
LANCASTER,  PA. 


PREFACE 

This  volume  has  been  written  to  fill  a  pressing  want ;  to 
give  a  practical  discussion  of  the  gasoline  propelled  com- 
mercial car  of  the  present  type,  and  to  present  this  subject 
in  the  plainest  possible  manner  by  the  use  of  numerous 
illustrations.  In  other  words,  this  work  is  compiled  for  the 
engineer,  who,  when  he  desires  information  on  current 
practice,  may  quickly  obtain  the  same  without  a  general 
study.  At  the  same  time  a  general  outline  of  the  underlying 
principles  is  given  for  the  student,  commercial  vehicle 
owner  and  operator  who  may  desire  to  familiarize  himself 
with  the  construction  of  the  various  units  that  make  up  the 
complete  vehicle. 

The  author  feels  confident  that  he  has  been  successful 
in  the  production  of  a  serviceable  treatise  on  the  subject  of 
Motor  Truck  design  and  construction. 

C.  T.  SCHAEFEK. 

ANDERSON,  IND., 
Sept.   1,  1919. 


415370 


CONTENTS 

CHAPTER.                                                                                                            PAGE. 
I.     THE  GENERAL  LAYOUT  OF  THE  CHASSIS ,  1 

II.    THE  MOTOR  TRUCK  ENGINE,  ITS  CONSTRUCTION  AND  LUBRICA- 
TION        6 

Two  and  Four  Cycle  Motors,  Cylinders,  Crank  Case,  etc., 
and  their  Functions. 

III.  THE  MOTOR  COOLING  SYSTEM 39 

Air  and  Water  Cooling-,  Natural  and  Forced  Cooling1  Sys- 
tems. Radiators  and  their  Mounting. 

IV.  CARBUBETION  AND  CARBURETORS    50 

Control  and  Vaporization  of  Fuel. 

V.     IGNITION  SYSTEMS   59 

High  Tension,  Low  Tension  and  Inductor  Magnetos.  Bat- 
tery and  Igniter  Systems. 

VI.     GOVERNORS  AND  SPEED  CONTROLLING  DEVICES   85 

Centrifugal,  Hydraulic  and  Automatic  Governors. 

VII.     THE  CLUTCH  AND  TRANSMISSION  95 

Cone,  Multiple  Disc,  and  Dry  Plate  Clutches.  Friction, 
Planetory,  Progressive  Sliding  and  Selective  Sliding 
Transmissions. 

VIII.    UNIVERSAL  JOINT  AND  PROPELLER  SHAFT 114 

Mechanical  and  Fabric  Type  Universals.  Solid  and  Tubu- 
lar Shafts.  Propeller  Shaft  Bearing  Mounting. 

IX.     THE    DIFFERENTIAL 125 

Spur,  Bevel  and  Worm  Gear  Types. 

X.     THE  FINAL  DRIVE    132 

Open  and  Enclosed  Chain  Drive.  Bevel,  Double  Reduction, 
Internal  and  Worm  Gear  Drive  Axles.  Method  of  taking 
Torque  and  Propulsion.  The  Hotchkiss  Drive. 

XI.     FRONT  AND  FOUR  WHEEL  DRIVES  162 

Tractors,  Gasoline  and  Electric  Types. 

XII.     MOTOR  TRUCK  BRAKES    172 

Internal  and  External  Types.  Jack  Shaft,  Propeller  Shaft, 
and  Rear  Wheel  Types. 

XIII.     THE   FRONT  AXLE    183 

Elliot,  Lemoine  and  Reversed  Elliot  Steering  Knuckles. 
Drop  Forged  and  Built-Up  Types. 

vii 


viii    MOTOE  TEUCK  DESIGN  AND  CONSTEUCTION 

CHAPTER.  PAGE. 

XIV.     STEERING  GEARS  AND  FUNDAMENTAL  PRINCIPLES  OF  STEERING 

MECHANISMS    192 

Spur,  Bevel  and  Worm  Gear,  Screw  and  Nut  Types.  Steer- 
ing- Gear  and  Linkage.  Construction  and  Layout. 

XV.     MOTOR  TRUCK  FRAMES    210 

Structural  and  Pressed  Steel,  Rigid  and  Flexible  Types. 

XVI.     POWER  PLANT  MOUNTINGS   220 

Unite  Power  Plant,  Individual  Mounting,  Sub  Frame 
Mounting.  Three  and  Four  Point  Suspension. 

XVII.     SPRINGS  AND  SPRING  SUSPENSIONS    230 

Spring  Types,  France  and  Axle  Mountings.  Overload  and 
Auxiliary  Spring's. 

XVIII.     THE  FUEL  SUPPLY  SYSTEM   244 

Gravity,  Pressure  and  Vacuum  Systems.  Gasoline  Tank 
Construction  and  its  Mounting-. 

XIX.     CONTROL    253 

Spark  and  Throttle  Control,  Clutch  and  Brake  Pedal 
Mounting1.  Gear  Shift  and  Brake  Control  Systems. 

XX.     THE  MUFFLER 265 

Muffler  Construction  and  Cut  Outs. 

XXI.     MOTOR  TRUCK  WHEELS   272 

Wood,  Pressed  and  Cast  Steel  Types,  for  Single  and  Dual 
Types. 

XXII.     MOTOR  TRUCK  TIRES  AND  RIMS   280 

Side  Flange,  Demountable,  S.  A.  E.  std.  Pressed-on  Single 
and  Dual  Types.  American  and  European  Sections. 
Care  of  Motor  Truck  Tires. 

XXIII.     ELECTRIC  LIGHTING  AND  STARTING  ON  COMMERCIAL  VEHICLES.   298 
Advantages    and   Disadvantages    of   Electrically   Equipped 
Trucks. 


MOTOR  TRUCK  DESIGN  AND 
CONSTRUCTION 


CHAPTEK  I 

THE  GENERAL  LAYOUT  OF  THE  CHASSIS 

ANY  commercial  vehicle  conforming  to  the  accepted  stand- 
ard of  construction  may  be  divided  in  two  parts,  the  chassis  and 
the  body.  The  chassis  or  running  gear  as  it  is  sometimes  called, 
consists  of  the  frame,  power  plant,  springs,  axles,  wheels,  brakes 
and  in  fact  all  units  which  enter  into  the  propulsion  and  control 
of  the  vehicle. 

There  are  three  general  types  of  chassis  when  classified  ac- 
cording to  the  type  of  power  plant,  the  gasoline,  the  steam  and 
the  electric.  The  gasoline  propelled  vehicle  is  by  far  the  most 
popular  and  will  be  considered  in  this  work. 

The  general  layout  of  the  chassis  covers  such  points  as  the  loca- 
tion of  the  driver's  seat  or  cab  in  relation  to  the  location  of  the 
power  plant,  which  controls  the  distribution  of  the  useful  or  pay 
load  of  the  vehicle.  This  affects  the  overall  length  and  turning 
radius  of  the  vehicle. 

The  principal  problem  confronting  the  commercial  vehicle 
designer  is  how  to  make  use  of  the  overall  length  of  the  chassis 
to  the  best  advantage,  considering  accessibility  and  all  other 
factors  which  enter  into  this  problem. 

Most  designers  have  placed  the  driver's  seat  back  of  the  motor. 
This  necessitates  the  making  of  the  total  length  of  the  machine 
somewhat  greater  than  it  would  be  for  the  same  capacity  when 
the  driver's  seat  is  placed  above  the  motor.  In  some  cases  a  com- 
promise is  effected  between  these  two  by  placing  the  driver's  seat 
and  steering  to  the  right  or  left  side  of  hood  which  encloses  the 
motor,  thus  saving  about  half  the  space  used  in  the  design  which 
has  the  seat  placed  in  back  of  the  motor. 

Advocates  of  each  type  have  a  number  of  arguments  in  favor 
of  their  design,  all  of  which  have  merit.  The  one  who  places  the 
2  1 


fcB:      ESIGN  AND  CONSTRUCTION 

seat  over  the  motor,  claims  that  by  this  arrangement,  the  load  is 
shifted  somewhat  forward  and  the  center  of  gravitjr  is  brought 
somewhat  nearer  the  center  of  the  machine.  This  is  claimed  to 
create  more  even  tire  wear  all  around  and  a  reduction  of  the  total 
overall  length  of  the  chassis.  The  last  is  an  advantage  as  it  per- 
mits a  shorter  wheel  base  and  turning  radius. 

Those  who  place  the  seat  back  of  the  motor  claim  that  in  the 
above  construction  too  much  weight  is  placed  on  the  front  axle, 
that  the  motor  is  more  accessible  and  that  it  is  placed  in  a  higher 
position  in  the  frame.  The  front  springs  can  be  made  somewhat 
lighter,  since  they  are  not  required  to  carry  as  large  a  percentage 
of  the  total  load.  And  being  lighter,  they  are  less  stiff  and  take 
the  shocks  of  the  road  more  readily,  which  tends  to  increase  the 
life  of  the  motor.  These  widely  varying  views  of  the  makers  are 
echoed  in  many  different  lengths  of  commercial  vehicles  which 
have  been  placed  on  the  market. 

Probably  no  single  feature  of  commercial  car  design  merits 
more  attention  than  does  that  of  arranging  the  power  plant  in 
such  a  manner  as  to  offer  the  user  motor  accessibility  in  the  great- 
est degree  consistent  with  reasonable  compact  design.  The  im- 
portance of  the  first  desideratum  will  be  admitted  by  anyone 
having  experience  in  the  operation  of  an  internal  combustion 
engine.  The  day  is  still  far  distant  when  a  gasoline  engine  may 
be  locked  in  a  box  and  with  a  supply  of  essence,  be  expected  to 
mote  satisfactorily  until  like  the  justly  famous  Shay,  its  multi- 
tudinous parts  give  out  simultaneously  as  a  result  of  legitimate 
wear.  The  desirability  of  compact  arrangement  will  be  endorsed 
as  a  purely  academic  proposition  and  will  be  heartily  subscribed 
to  as  a  thoroughly  practical  feature  by  truck  operators,  who  have 
had  to  deal  with  metropolitan  street  and  garage  conditions. 

As  far  as  the  power  plant  arrangement  is  concerned  American 
makers  have  formed  themselves  into  three  distinct  classes.  First, 
the  class  comprising  those  who  place  accessibility  above  all  other 
considerations.  Second,  the  class  comprising  those  whose  great- 
est satisfaction  arises  from  the  contemplation  of  a  design  in 
which  the  compact  arrangements  of  parts  is  accentuated.  Third, 
the  class  comprising  those  who  have  attempted  to  effect  a  com- 
promise between  the  above  two  types,  to  secure  both  accessibility 
and  compactness. 

Advantages  of  Placing  Motor  Under  the  Hood. — A  layout  of 
the  trend  of  the  first  class  of  commercial  car  design  is  depicted  in 


THE  GENEEAL  LAYOUT  OF  THE  CHASSIS   3 

Fig.  1.  It  will  be  noted  that  the  motor  is  carried  under  a  re- 
movable hood  in  front  of  the  driver's  seat  and  control  elements, 
being  typical  of  current  passenger  car  chassis  design.  The  load- 
ing platform  is  divided  into  approximately  equal  parts  fore  and 
aft  of  the  rear  axle.  This  design  permits  of  easy  access  to  the 
motor  and  accessory  parts  from  both  sides  and  top,  making  it 


FIG.  3. 
THREE  PROMINENT  TYPES  OF  CHASSIS. 

equal  in  point  of  accessibility  to  passenger  cars.  The  driver's 
seat  is  also  accessible  while  the  clutch  and  change  gear  can  be 
easity  reached  through  the  floor  board  opening  when  they  form 
a  unit  with  the  motor.  The  greater  percentage  of  the  paying 
load  is  concentrated  upon  the  rear  or  driving  wheels,  resulting  in 
good  traction  and  easy  steering.  This  construction  also  results 
in  a  pleasing  appearance,  which  is  of  some  advantage  in  smaller 
vehicles,  which  are  used  to  some  extent  as  an  advertising  feature. 


4   MOTOE  TKUCK  DESIGN  AND  CONSTRUCTION 

Disadvantages  of  this  Type. — Like  all  other  constructions  the 
above  type  offers  certain  disadvantages.  The  overall  length  of 
the  vehicle  must  be  greater  in  order  to  permit  the  location  of  the 
motor  under  a  removable  hood.  In  many  cases  this  added  length 
does  not  operate  as  a  decided  disadvantage  for  average  applica- 
tion in  which  the  machine  must  be  maneuvered,  in  narrow  thor- 
oughfares, backed  up  to  curbings  and  garaged  in  valuable  space, 
every  inch  of  added  length  makes  itself  felt  in  the  owner's  purse. 
With  the  question  of  load  distribution  it  may  be  said  that  care- 
less freight  handlers  are  just  as  likely  to  place  the  light,  bulky 
portion  of  a  miscellaneous  load  forward  of  the  axle,  and  to  burden 
the  overhang  with  heavy  material,  occupying  little  space,  as  they 
are  to  reverse  the  loading.  Concentration  of  both  driving  and 
load  stresses  to  a  maximum  degree  upon  one  pair  of  tires  causes 
loss  as  far  as  tire  economy  is  concerned. 

Motor  Under  the  Seat  Type. — Turning  now  to  the  type  of  con- 
struction representative  of  the  second  class  of  design,  we  find 
illustrated  in  Fig.  2,  a  vehicle  in  which  the  driver's  seat  and  con- 
trolling elements  are  superimposed  upon  the  motor  space,  the 
load  being  apportioned  fore  and  aft  the  rear  axle  in  an  approxi- 
mate ratio  of  2  to  1.  The  result  of  this  load  distribution  is  that 
it  does  not  permit  of  a  traction  ratio  so  high  as  does  the  pre- 
viously described  type,  and  steering  is  perhaps  less  sensitive. 
But  when  the  high  friction  coefficient  of  rubber  is  considered 
upon  average  road  surface  and  the  fact  that  roller  bearing  steer- 
ing heads  are  to  be  found  in  most  commercial  car  axles  of  mod- 
ern design,  then  these  two  conditions  become  relatively  important. 
In  respect  to  the  load  distribution,  the  latter  construction  pos- 
sesses advantages  over  the  first  type.  For  a  given  loading  space 
the  construction  in  Fig.  2  permits  of  marked  compactness  in 
overall  length,  with  the  attendant  advantage  of  ease  of  handling, 
minimum  projection  into  through  fares  when  backed  up  to  a 
curve  and  economy  of  garage  space. 

Lack  of  Accessibility. — These  relative  advantages  are  gained 
at  the  expense  of  motor  accessibilit}^  Doors  or  removable  panels 
are  usually  fitted  to  allow  access  to  the  motor  from  the  side, 
while  floor  boards  permit  limited  access  from  the  top.  When 
front  fenders  are  provided  the  access  from  the  sides  is  also  ma- 
terially reduced.  This  notable  lack  of  accessibility  arises,  first, 
from  the  necessity  for  rigid  and  fairly  bulky  superstructure  for 
carrying  the  driver's  seat  and  second,  from  the  fact  that  a  maze 


THE  GENERAL  LAYOUT  OF  THE  CHASSIS    5 

of  control  levers,  brackets  and  rods  are  frequently  located  in  the 
space  which  should  be  reserved  for  access  to  the  motor  and  its 
accessories.  Many  trucks  show  a  marked  improvement  in  this 
construction,  however,  at  best  it  leaves  much  to  be  desired  in  the 
way  of  accessibility. 

Type  Three  a  Combination. — There  is  still  another  type,  Fig. 
3,  which  has  been  introduced  several  years  ago,  in  which  an 
attempt  is  made  to  combine  the  advantages  of  the  first  and  sec- 
ond types  is  apparent.  This  has  been  accomplished  in  a  meas- 
ure, by  mounting  the  motor  in  a  more  or  less  accessible  position 
between  the  two  seats.  A  removable  hood  is  generally  fitted,  but 
the  net  result  is  almost  invariably  inferior  from  a  standpoint  of 
accessibility  to  the  construction  shown  in  Fig.  1,  although  from 
the  same  viewpoint  it  is  an  improvement  over  Fig.  2.  The  ad- 
vantage of  longitudinal  compactness  is  retained,  moreover  the 
weight  is  well  distributed  between  the  front  and  rear  axles. 

In  making  the  illustrations,  the  writer  has  taken  pains  to  have 
the  wheel  base  (i.  <?.,  center  of  front  wheel  to  center  of  rear 
wheel),  and  the  length  of  the  loading  in  equal  proportions  in  all 
illustrations  so  that  a  good  idea  can  be  obtained  as  to  relative 
overall  length  and  weight  distribution. 

It  can  readily  be  seen  that  in  the  point  of  overall  length,  the 
construction  which  embodies  placing  the  driver's  seat  over  the 
motor  has  the  advantage  of  requiring  less  length  than  the  other 
two  types.  While,  on  the  other  hand,  the  question  may  be  asked, 
are  the  advantages  to  be  gained  by  placing  the  driver's  seat  over 
the  motor  great  enough  to  outweigh  those  claimed  for  other  con- 
structions 1 

The  general  advantage  of  either  construction  presents  itself 
when  the  conditions  of  operations  are  considered.  The  vehicle 
may  be  operated  in  districts  when  traffic  is  congested,  which 
would  favor  class  two,  while  on  the  other  hand  accessibility  may 
be  the  chief  point  to  be  considered,  which  then  would  favor  class 
one.  While  certain  conditions  may  suggest  the  selection  of  class 
three.  In  the  smaller  vehicles  class  one  is  greatly  desired  owing 
to  its  pleasing  appearance  when  fitted  with  expense  bodies. 

From  the  above  it  can  readily  be  understood  that  the  construc- 
tion of  a  vehicle  is  somewhat  depended  upon  the  conditions  of 
operation  and  nature  of  the  work  it  has  to  accomplish. 


CHAPTEE  II 

THE  MOTOR  TRUCK  ENGINE— ITS  CONSTRUCTION  AND 
LUBRICATION 

Two  and  Four-cycle  Multi-cylinder  Motors. — This  term  cycle 
is  defined  as  the  cycle  of  operations  or,  in  other  words,  the  suc- 
cessive actions  of  the  working  fluid  of  a  heat  engine  upon  the 
piston  and  of  the  piston  upon  the  working  fluid  commencing 
when  a  certain  relationship  between  the  two  exists  and  ending 
with  the  next  recurrence  of  the  same  relationship;  or,  in  other 
words,  any  series  of  events  occurring  in  succession,  which  goes  to 
make  up  a  complete  operation. 

.  There  are  four  things  which  must  occur  in  an  engine  cylinder 
in  succession  before  it  can  repeat.  As  soon  as  the  explosion  oc- 
curs, the  gas  must  expand,  which  forces  the  piston  down  to  the 
end  of  its  stroke.  Upon  the  completion  of  this  stroke  or  the  next 
up  stroke  the  spent  gases  must  be  gotten  rid  of  by  forcing  them 
out  of  the  cylinders;  then  a  fresh  charge  must  be  drawn  in  and 
compressed  before  the  explosion  again  takes  place. 

This  series  of  operations  is  termed  the  cycle  of  operations. 
There  are  two  types  of  gasoline  motors,  one  comprising  that  type 
which  has  a  power  stroke  every  revolution,  which  is  termed  the 
two-cycle  or  two-stroke  type,  and  the  other  which  has  a  power 
stroke  every  other  revolution,  termed  the  four-cycle  or  four- 
stroke  type. 

The  Two-cycle  Type. — As  mentioned  above,  the  characteristic 
feature  of  the  two-cycle  motor  is  that  there  is  an  explosion  every 
revolution  on  the  down  stroke  of  the  piston.  Another  feature  of 
this  type  of  motor  is  that  the  gas  must  be  precompressed,  which 
is  generally  accomplished  by  admitting  it  to  the  crank  case  before 
it  reaches  the  cylinders. 

There  are  two  general  types  of  two-cycle  motors,  known  as 
the  two-  and  three-port  types,  so  called,  by  the  number  of  ports 
in  the  cylinders,  which  permit  gas  to  enter  and  to  escape  after 
combustion.  The  three-port  type  is  mostly  used  in  motor  truck 
work,  while  the  two-part  type  is  strictly  a  low-speed  motor  and 
best  adapted  to  marine  work,  where  speed  is  a  minor  considera- 

6 


THE  MOTOK  TRUCK  ENGINE         7 

tion.  In  depicting  the  operations  of  a  two-cylinder  motor,  the 
three-port  type  will  be  considered,  as  it  would  be  useless  to  use 
considerable  space  on  a  subject  which  is  of  no  interest. 

In  four-cycle  motors  the  four  events  mentioned  above,  i.e., 
ignition,  exhaust,  intake  and  compression,  take  place  between  the 
piston  head  and  the  head  of  the  cylinder,  but  in  the  two-cycle 
type  the  crank  case  is  made  air  tight  and  performs  part  of  the 
work  of  getting  the  gas  ready  to  ignite. 

The  successive  operations  of  the  two-cycle  motors  are  as  fol- 
lows: While  the  piston  is  traveling  upward  in  the  cylinders  it 
creates  a  partial  vacuum  in  the  crank  case,  and  when  it  reaches 
a  certain  point  it  uncovers  the  intake  port  A  in  the  walls  of  the 

CYCLE  OF  OPERATIONS  IN  A  Two  CYCLE  MOTOR. 


FIG.  4.                      FIG.  5.  FIG.  6. 

Crank  Case  In-  Expansion  and  Exhaust  and 

let    and    Cylinder          Exhaust.  Transfer     of 

Compression.  Gas. 

cylinder,  through  which,  by  reason  of  this  vacuum,  it  permits  a 
charge  of  gas  to  enter  the  crank  case  from  the  carbureter.  This 
stroke  is  illustrated  in  Fig.  4,  while  Fig.  5  depicts  the  next  down 
stroke  of  the  piston.  Daring  this  down  stroke,  the  charge  is 
partly  compressed  in  the  crank  case.  As  the  piston  reaches  the 
bottom  of  its  stroke,  it  uncovers  the  port  B  in  the  cylinder  wall, 
which  communicates  with  the  crank  case  and  is  called  the  transfer 
port,  thus  permitting  the  charge  in  the  crank  case  to  enter  the 
cylinder.  Shortly  after  the  piston  starts  on  its  up  stroke  it  closes 
this  transfer  port,  and  during  the  remainder  of  this  stroke  the 
charge  is  compressed  within  the  cylinder  and  as  it  reaches  the 
top  of  its  stroke  the  charge  is  ignited,  expands  and  forces  the 
piston  downward.  As  the  piston  reaches  the  bottom  of  its  stroke 
the  exhaust  port  C  is  opened,  and  the  spent  gases  which  are  still 


8   MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

under  considerable  pressure  escape  through  this  port.  This  ex- 
haust port  opens  a  trifle  earlier  than  the  transfer  port,  permit- 
ting considerable  of  the  spent  gases  to  escape  before  the  fresh 
charge  is  admitted  to  the  cylinders.  This  is  illustrated  in  Figs.  5 
and  6.  It  is,  of  course,  impossible  to  completely  scavenge  the 
cylinders  and  prevent  the  fresh  charge  from  escaping  through 
the  port  C\  however,  the  piston  has  a  deflector  D  which  is  in- 
tended to  deflect  the  incoming  gas  upward  and  reduce  the  loss  to 
a  minimum.  This  deflector  must  be  placed  opposite  the  exhaust 
port. 

From  the  above  we  can  readily  understand,  that  when  the 
charge  is  being  compressed  in  the  cylinders  on  the  up  stroke  of 
the  piston  and  before  ignition  takes  place,  a  fresh  charge  is  per- 
mitted to  enter  the  crank  case  and  when  ignition  takes  place  the 
gas  expands,  forcing  the  piston  downward  and  nearing  the  bottom 
of  its  stroke  it  uncovers  first  the  exhaust  port,  permitting  a  fresh 
charge  to  enter  the  cylinder,  after  which  compression  within  the 
cylinder  again  takes  place,  thus  completing  all  four  operations  in 
one  revolution  of  the  crank  shaft  or  two  strokes  of  the  piston, 
crank  case  intaking  and  cylinder  compression  on  the  up  stroke, 
expansion,  exhaust  and  transfer  of  charge  from  crank  case  on  the 
down  stroke. 

The  Four-cycle  Type. — The  same  operations  occur  in  the  four- 
cycle type  of  motor;  however,  they  require  two  complete  revolu- 
tions of  the  crank  shaft  or  four  piston  strokes.  This  comprises 
the  following  operations  as  mentioned  below:  (1)  Admission  of 
charge  to  the  cylinder,  (2)  compression  of  charge  within  the 
cylinders,  (3)  ignition  and  expansion  of  charge,  (4)  exhausting 
spent  gases. 

In  four-c}^cle  motors  the  inlet  and  exhaust  of  the  charge  is 
entirely  controlled  by  valves  instead  of  the  piston  and  ports  in 
the  two-cycle  motor.  During  the  past  few  years  numerous  types 
of  valves  have  been  used,  such  as  the  piston  type,  which  may  be 
compared  with  a  small  piston  opening  and  closing  the  ports  at 
the  proper  time,  sliding  sleeve,  operated  on  the  same  principle, 
and  poppet  valves  which  are  opened  by  a  cam  mechanism.  The 
sleeve  and  piston  valve  motors  have  been  experimented  with  for 
pleasure  car  work;  however,  in  commercial  cars  poppet  valve 
motors  have  been  almost  exclusively  used  in  this  country,  and  the 
writer  will  confine  his  discussion  to  this  type  of  four-cycle  motor. 
As  mentioned  above,  the  first  stroke  of  a  four-cycle  motor  is  the 
admission  or  intake  stroke. 


THE  MOTOR  TRUCK  ENGINE 


9 


The  piston  travels  downward  in  the  cylinder  and  at  some 
point  in  the  wall  of  the  combustion  chamber  an  inlet  valve  is 
located,  which  at  the  proper  time  opens  and  places  the  combus- 
tion chamber  in  communication  with  the  carburetor  (see  Fig.  7). 
As  this  valve  opens  the  piston  has  moved  downward  a  short  dis- 
tance, and  a  vacuum  has  been  formed  with  the  cylinder  which 
creates  a  suction  and  permits  the  charge  to  enter.  These  valves 
were  formerly  operated  by  this  vacuum  within  the  cylinder  and 

CYCLE  OF  OPERATIONS  IN  A  FOUR  CYCLE  MOTOR. 


FIG.  7. 
Intake 
Stroke. 


FIG.  8. 

Compression 

Stroke. 


FIG.  9. 
Power 
Stroke. 


FIG.  10. 
Exhaust 
Stroke. 


a  light  spring  to  close  them  when  suction  ceased.  This  type  was 
known  as  the  automatic  intake  valve,  but  was  discarded  some 
years  ago,  as  it  presented  numerous  disadvantages.  At  the  pres- 
ent time  mechanically  operated  intake  valves  are  used,  which  are 
opened  and  closed  by  mechanical  connection  with  the  motor  crank 
shaft  at  the  proper  time. 

This  valve  remains  open  until  piston  has  passed  the  bottom 
of  its  stroke,  and  shortly  after  the  piston  has  started  on  its  up 
stroke  it  closes  and  remains  closed  during  the  completion  of  this 
up  stroke.  During  this  up  stroke  the  charge  is  compressed  within 
the  combustion  chamber  (which  is  sometimes  termed  the  com- 
pression space)  and  prepared  for  ignition.  So  far  the  piston  has 
made  two  complete  strokes,  and  the  crank  shaft  one  complete 
revolution,  while  two  operations  have  been  completed  within  the 
cylinders,  this  second  operation  being  shown  in  Fig.  8. 

Upon  the  completion  of  the  compression  stroke  the  gas  is 
ignited  by  introducing  an  electrical  spark  to  occur  within  the 


10      MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

combustion  chamber.  When  the  charge  is  ignited  the  pressure 
rises  to  between  four  or  five  times  what  it  was  previously,  caus- 
ing the  gases  to  expand  and  thus  forcing  the  piston  downward 
and  converting  the  heat  of  these  gases  into  useful  energy  or 
power.  This  stroke,  known  as  the  power  stroke,  is  illustrated  in 
Fig.  9. 

When  the  piston  reaches  the  bottom  of  its  stroke  the  exhaust 
begins  to  open  and  the  spent  gases  escape  rapidly.  This  exhaus- 
tion of  spent  gases  continues  all  through  the  following  return 
stroke  of  the  piston,  the  valve  remaining  open  until  the  piston 
has  again  moved  downward  a  slight  distance  and  then  both  valves 
remain  closed  for  a  short  period  to  create  the  vacuum  which 
causes  the  suction  of  gases  from  the  carburetor  on  the  intake 
stroke,  and  permitting  the  motor  to  again  resume  its  cycle  of 
operations. 

The  exhaust  valves  are  always  operated  by  mechanical  con- 
nection with  the  motor  crank  shaft,  similar  to  the  intake  valve; 
however,  timing  is  different,  as  they  must  remain  open  longer 
than  the  intake.  In  two-cycle  motors  the  exhaust  and  transfer 
ports  must  be  placed  opposite  each  other ;  however,  the  valves  of 
the  four-cycle  type  of  motor  may  be  placed  in  various  positions, 
as  both  valves  are  never  open  at  the  same  time.  Fig.  10  clearly 
illustrates  this  point.  The  exhaust  valve  is  shown  and  the  piston 
is  traveling  upward,  while  when  the  intake  valve  is  open  the 
piston  must  travel  downward. 

In  presenting  these  illustrations  the  writer  has  depicted  valves 
on  both  sides,  so  as  to  simplify  the  illustrations  as  much  as  pos- 
sible. In  the  various  motors  the  following  valve  arrangements 
may  be  found:  The  valves  may  be  on  opposite  sides  of  the  cyl- 
inder, which  is  called  the  T-head  type  while  in  others  they  are 
located  side  by  side,  and  known  as  the  L-head  type;  they  are 
also  located  in  the  cylinder  heads,  and  by  combination  of  one 
valve  in  the  head  and  the  other  in  the  side;  however,  the  first 
three  are  the  most  popular  types. 

Advantages  and  Disadvantages  of  Both  Types  of  Motors. — In 

the  two-cycle  motor  we  find  that  both  the  exhaust  and  transfer 
ports  are  open  together  for  certain  periods,  and  it  can  readily  be 
understood  that  since  we  are  performing  the  four  operations  in 
two  strokes  of  the  piston,  the  time  required  for  each  operation  is 
limited.  It  was  also  stated  that  the  exhaust  port  opened  slightly 
before  the  transfer  port  and  that  a  fresh  charge  was  admitted 


THE  MOTOK  TEUCK  ENGINE         11 

before  the  spent  gases  had  entirely  escaped.  From  this  we  can 
assume  that  all  the  spent,  gases  do  not  escape  and  that  there  is  a 
possibility  of  part  of  the  fresh  charge  escaping  through  the  ex- 
haust port,  and  the  fresh  charge  becoming  deluged  with  the  spent 
gases  which  do  not  entirely  escape.  In  comparing  the  exhaust 
and  intake  periods  of  both  types  of  motors,  we  find  that  these 
periods  cover  but  approximately  one-half  the  time  in  two-cycle 
motors  than  in  the  four-cycle  type.  The  combination  of  these 
operations  and  the  short  periods  naturally  permit  of  less  fuel 
economy  in  the  two-cycle  motor.  That  considerable  fuel  is  wasted 
has  been  proven  by  exhaust  gas  analysis  on  numerous  occasions. 

In  the  four-cycle  type  we  get  a  greater  charge  in  the  cylinders 
due  to  the  longer  period,  as  one  complete  stroke  of  the  piston  is 
required  and  this  is  maintained  during  the  compression  stroke 
as  both  valves  remain  closed.  This  is  of  great  importance  in 
high-speed  motors,  as  even  with  the  long  periods  intake  becomes 
very  short  when  the  higher  engine  speeds  are  reached  and  much 
less  gas  enters  the  cylinders.  Even  in  lower  engine  speeds  it  pre- 
sents advantages.  The  cylinder  also  maintains  its  full  volume 
until  after  combustion  occurs  and  the  exhaust  gases  are  forced 
out  of  the  cylinder  by  the  return  stroke  of  piston,  during  which 
time  the  intake  valve  remains  closed  and  no  dilution  of  gases 
occurs.  Of  course,  some  spent  gases  remain  in  the  cylinders  of  a 
four-cycle  motor ;  however,  the  quantity  is  much  less  and  does  not 
have  much  effect  on  the  next  fresh  charge. 

There  is  also  considerable  power  loss  in  two-cycle  motors,  due 
to  leaky  pistons,  crank  case  joints  and  cylinders  and  bearing 
journals.  This  is  of  considerable  importance,  as  the  gas  is  partly 
compressed  in  the  crank  case  and  can  escape  through  the  exhaust 
port,  should  the  rings  leak  or  through  the  various  joints,  should 
they  not  remain  air  tight. 

In  four-cycle  motors  power  is  lost  through  leaky  pistons,  and 
valves;  however,  it  is  not  as  great  and  is  of  little  importance  as 
the  engine  will  continue  to  run  and  develop  a  small  amount  of 
power.  This  is  not  the  case  with  the  two-cycle,  as  in  the  first 
place  the  fresh  charge  is  somewhat  limited  and,  second,  it  can 
escape  before  it  reaches  the  cylinder,  sometimes  causing  complete 
stoppage  of  the  engine. 

Leaky  valves  can  readily  be  reground  at  a  small  cost  without 
dismantling  the  engine,  while  to  eliminate  leaks  in  the  two-cycle 
means  complete  dismantling,  which  is  an  expensive  item,  as  new 
bearings  must  be  provided  in  case  they  permit  gas  to  escape,  it 


12      MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

being  impossible  to  adjust  them  with  shims  and  retain  an  air- 
tight case.  Crank  case  leaks  are  also  of  serious  nature,  as  the 
motor  must  be  dismantled  in  order  to  replace  the  gaskets  at  the 
various  joints.  Replacing  rings  is  probably  of  equal  expense  in 
both  types. 

The  manufacturing  cost  is  lower  in  the  two-cycle  type,  while 
it  is  also  somewhat  more  simple,  due  to  the  absence  of  the  valves 
and  their  operating  mechanism.  As  there  are  fewer  parts  and 
the  limitations  of  their  proportions  also  means  lower  weight  per 
horse  power  for  the  two-cycle  type,  and  it  is  also  claimed  that 
they  develop  somewhat  more  power  and  have  a  better  mechanical 
balance.  However,  these  features  are  obtained  at  considerable 
expense  in  maintenance  and  it  would  seem  that  the  logical  com- 
mercial car  motor  is  one  which  provides  the  lowest  maintenance 
cost  in  proportion  to  the  work  done,  which  refers  to  the  four- 
cycle type. 

The  four-cycle  motor  also  has  its  disadvantages,  being  more 
complicated,  more  expensive  to  build  and  perhaps  its  weakest 
point  is  the  valves;  however,  they  are  readily  accessible,  and  do 
not  mean  much  expense  in  regrinding  or  replacements.  Leaky 
inlet  valves  alone  permit  the  diluting  of  the  charge  with  spent 
gases  and  indirectly  reduce  the  power  of  the  motor.  The  valve 
operating  mechanism  of  course  is  a  source  of  complication  and 
expense  and  would  be  eliminated  if  this  could  be  done  without 
too  great  a  sacrifice  in  other  directions. 

It  is  also  a  well-known  fact  that  carburetion  is  more  difficult 
in  the  two-cycle  motor,  which  may  be  due  to  the  fact  that  the 
suction  of  the  carburetor  is  more  rapid  and  uneven  in  this  type 
than  in  the  four-cycle  type. 

Two-cycle  motors  also  require  considerably  more  lubricating 
oil  and  can  not  be  lubricated  by  splash,  owing  to  crank-case  com- 
pression. Forced  lubrication  from  an  outside  source  must  be 
used.  While  the  two-cycle  engine  has  been  built  for  the  past 
twenty  or  thirty  years,  it  has  not  been  deemed  worthy  of  the 
serious  attention  of  many  engineers,  and  it  has  not  yet  reached 
anything  near  the  standardization  and  perfection  of  the  four- 
cycle engine. 

Multi-cylinder  Engines. — For  small  moderate  powers  a  single- 
cylinder  engine  possesses  the  advantages  of  the  simplest  possible 
construction,  inexpensive  to  manufacture  and  maintain,  and  more 
economical  in  the  use  of  fuel.  Along  with  its  advantages,  how- 
ever, it  possesses  two  inherent  defects,  particularly  from  the 


THE  MOTOR  TRUCK  ENGINE         13 

standpoint  of  its  use  in  commercial  cars,  for  which  reason  it  is 
new  seldom  employed.  In  discussing  the  cycle  of  operations  it 
was  stated  the  power  impulses  were  irregular,  due  to  the  fact  that 
a  power  stroke  occurs  every  other  stroke,  or  every  fourth  stroke 
and  that  the  gases  which  are  compressed  in  the  cylinders  require 
a  certain  portion  of  power  to  accomplish. 

Therefore,  in  order  to  keep  the  engine  running  at  a  fairly 
uniform  speed  against  a  nearly  constant  resistance  it  is  necessary 
to  employ  a  heavy  fly-wheel  in  which  some  of  the  energy  liberated 
on  the  power  stroke  can  be  stored,  to  be  given  out  again  during 
the  idle  strokes. 

A  single-cylinder  motor  is  sadly  lacking  in  mechanical  bal- 
ance and  the  vibrations  are  great.  These  vibrations  are  due  to 
the  reactions  of  the  explosion  and  inertia  forces.  In  a  single- 
cylinder  motor  the  entire  reciprocating  mass  (i.e.,  the  piston  with 
its  parts,  the  connecting  rod,  bearing  and  crank  pin),  is  in  a 
single  unit  and  the  reaction  of  the  inertia  force  of  the  parts  pro- 
duces a  strong  vibrating  effect,  while  in  multi-cylinder  motors 
the  reciprocating  masses  can  be  divided  into  several  units  and  so 
arranged  as  to  move  in  opposite  directions,  thereby  neutralizing 
the  inertia  effects. 

The  two-cylinder  motors  present  some  advantages  over  the 
single-cylinder  type.  However,  their  use  is  also  somewhat  lim- 
ited, and  it  is  only  a  question  of  time  until  all  commercial  cars 
will  be  equipped  with  four-cylinder  motors.  The  two-cylinder 
type  presents  an  advantage  over  the  single  cylinder  in  that  there 
are  two  reciprocating  masses,  so  arranged  that  one  effects  the 
force  of  the  other.  However,  perfect  balance  has  not  been  reached 
and  vibrations  are  still  noticeable  to  a  considerable  degree. 

In  the  four-cylinder  motors  now  extensively  used  in  com- 
mercial cars,  the  two  inside  reciprocating  masses  work  together 
and  the  two  outside  work  together.  However,  they  are  so  ar- 
ranged that  the  two  inner  ones  always  set  against  the  two  outer 
ones.  Although  they  are  equal  in  weight,  they  operate  in  oppo- 
site directions. 

The  turning  movement  of  a  four-cylinder  motor  is  also  much 
more  uniform  than  that  of  a  one  or  two-cylinder  motor,  hence 
the  torque  reaction  and  vibration  due  to  it  are  much  smaller. 
This  four-cylinder  type  when  properly  constructed  meets  the  re- 
quirements of  vibrationless  running  quite  satisfactorily. 

Types  of  Cylinders  and  their  Parts. — From  what  has  been  pre- 
viously said  of  the  piston  strokes  and  crank  shaft  revolution  it 


14      MOTOE  TEUCK  DESIGN  AND  CONSTEUCTION 


can  readily  be  understood  that  the  piston  travels  up  and  down 
within  the  cylinder,  while  the  crank  shaft  rotates  in  its  bearings, 
in  order  to  impart  a  turning  effort  to  the  rear  or  driving  wheels 
of  the  vehicle  through  suitable  power  transmitting  units.  This 
conversion  of  reciprocating  into  rotary  motion  will  be  depicted 
below. 

Advantages  and  Disadvantages  of  Different  Types  Discussed. 

— The  construction  of  a  gasoline  engine  is  quite  simple  in  its  ele- 
mentary form,  being  comprised  of  a  cylinder,  a  piston  provided 

with  rings  operating  within 
the  cylinder,  a  pair  of  valves 
or  ports  which  permit  at  the 
proper  time  the  entrance  and 
escape  of  the  gases,  a  connect- 
ing rod  which  connects  the  pis- 
ton with  the  crank  shaft,  a  case 
which  supports  the  crank  shaft 
and  carries  the  valve  operating 
mechanism,  this  valve  mechan- 
ism being  comprised  of  a  shaft 
with  separate  or  integral  cams, 
suitable  shaft  bearings  and  a 
train  of  gears  driven  from  the 
crank  shaft;  also  a  set  of  push 
rods  which  act  as  intermediate 
members  between  the  valve 
stems  and  the  cams. 

The    cylinders    are    usually 
castings     made      from     close- 


FIG.  11.  Section  of  a  Cylinder. 
A  Combination  of  Valve-in-Head 
and  L-Head  Type. 


grained  iron  provided  with 
either  water  jackets  for  water 
cooling  or  fins,  sometimes  called 
ribs  for  air  cooling.  They  are  open  at  one  end,  while  the  other 
end  is  closed,  forming  the  combustion  chamber,  in  which  the 
valves  are  located.  The  walls  of  this  cylinder  are  made  very 
smooth  and  are  generally  brought  to  a  high  polish  by  grinding, 
so  that  the  piston  with  its  rings  can  slide  freely  within  the  cylin- 
der. This  cylinder,  with  its  parts,  is  bolted  to  the  crank  case, 
which  carries  the  various  other  parts.  Fig.  11  depicts  a  cylinder 
in  section  showing  its  various  parts. 

The  pistons  of  gasoline  engines  are  of  the  trunk  type,  as  illus- 


THE  MOTOE  TEUCK  ENGINE 


15 


trated  in  Fig.  12,  being  somewhat  longer  than  the  diameter  of 
the  cylinder.  Near  the  center  of  the  piston  bosses  are  formed, 
which  receive  the  piston  pin  or  gudion  pin  as  it  is  sometimes 
termed.  Near  the  top  three  or  four  grooves  are  turned  into  the 
piston  which  receive  the  eccentric  piston  rings,  while  near  the 
lower  end  oil  grooves  are  turned  for  distributing  and  collecting 
the  surplus  lubricating  oil  on  the  cylinder  walls.  These  pistons 
are  made  a  trifle  smaller  in  diameter  than  the  cylinder  to  permit 
of  the  expansion  of  the  metal  on  the  power  stroke,  while  rings, 
carried  on  the  piston,  permit  of  flexibility,  so  that  the  gases 
cannot  escape  by  the  piston. 


FIG.  12.     Connecting-  Rod,   Piston  Pin  Crank   Shaft,  Flywheel  and  Main 
Bearings  of  a  Four  Cylinder  Engine. 

The  crank  shaft  is  a  horizontal  steel  shaft  carried  in  journals, 
or  bearings,  inside  of  the  crank  case,  while  offsets  corresponding 
with  the  number  of  cylinders  are  provided.  These  offsets  are 
termed  the  crank  pins  and  carry  the  large  end  of  the  connecting 
rod  and  its  bearings;  it  is  also  provided  with  a  taper  or  flanged 
end  to  which  the  flywheel  is  attached  by  means  of  a  key  or  nut 
or  bolts. 

The  connecting  rod  forms  an  intermediate  link  between  the 
piston  and  the  crank  shaft.  It  is  usually  made  a  drop  forging, 


16      MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

the  small  end  carrying  a  bearing  for  the  piston  pin,  while  the 
large  end  is  divided  and  carries  the  crank  pin  bushing. 

It  was  stated  above  that  the  piston  travel  was  a  reciprocating 
motion  while  the  crank  shaft  revolution  was  a  rotary  motion,  and 
that  it  was  necessary  to  convert  this  reciprocating  motion  into 
rotary  motion,  for  the  reason  stated  above.  This  conversion  of 
motion  is  performed  by  the  connecting  rod,  as  it  is  hinged  to  both 
piston  and  crank  shaft  and  this  conversion  of  motion  may  be  de- 
picted as  follows: 

When  the  piston  is  at  its  upper  point  of  travel  in  the  cylinder 
the  cr*ank  pin  is  standing  vertical  above  the  crank  shaft,  but  as 
the  piston  and  connecting  rod  move  downward  under  the  influ- 
ence of  the  expanding  gases  within  the  cylinders,  the  crank  pin 
is  constrained  and  revolves  downwardly,  thus  turning  the  crank 
shaft.  The  crank  pin  passes  through  its  horizontal  position  and 
as  the  motion  of  the  piston  and  connecting  rod  continues,  finally 
reaches  a  position  vertically  below  the  crank  shaft,  the  piston  at 
this  moment  being  at  its  lowest  point  and  the  crank  shaft  has 
been  revolved  through  one-half  revolution.  As  the  piston  begins 
to  move  upward  upon  its  return  stroke  the  crank  shaft  is  again 
constrained  by  the  connecting  rod  to  revolve  and  gradually  ap- 
proaches and  passes  its  other  horizontal  position  arid  finally, 
when  the  piston  is  all  the  way  up,  the  crank  pin  has  reached  its 
original  vertical  position  again,  having  turned  the  crank  pin 
through  one  complete  revolution. 

Thus  it  can  readily  be  understood  that  the  upper  end  or  piston 
pin  end  of  the  connecting  rod  reciprocates  in  harmony  with  the 
piston,  while  its  lower  end  or  crank  pin  end  rotates  in  harmony 
with  the  crank  pin,  converting  the  reciprocating  motion  of  the 
piston  into  rotary  motion  of  the  crank  shaft.  It  should  be  re- 
membered that  in  multi-cylinder  engines  the  explosion  force  in 
one  cylinder  will  move  the  piston  downward  in  the  other  cylinder 
which  is  paired  with  it  and  is  on  the  intake  stroke.  Thus  in  Fig. 
12  the  two  end  crank  pins  are  vertical  and  while  the  right  hand 
one  is  being  forced  downward  it  carries  the  left-hand  pin  with  it. 
The  left-hand  cylinder  being  on  the  intake  stroke,  it  also  forces 
the  two  lower  crank  pins  upward,  the  corresponding  cylinder  of 
one  of  these  being  on  the  compression  stroke  and  the  other  on  an 
exhaust  stroke.  In  this  way  the  right-hand  pin  is  revolved  up- 
ward when  the  lower  pin  on  the  compression  stroke  begins  to 
move  downward  on  the  next  power  stroke  which,  as  stated  in  the 


THE  MOTOR  TRUCK  ENGINE         17 

previous  article,  follows  compression.    This  operation  is  followed 
by  all  crank  pins  on  the  various  power  strokes  of  the  pistons. 

In  the  single-cylinder  motors  this  return  motion  is  obtained 
by  the  storage  of  energy  in  the  flywheel  on  the  power  stroke, 
which  liberates  itself  on  the  idle  strokes  of  the  piston.  This  was 
discussed  under  the  heading  of  multi-cylinder  engines. 

The  operation  of  the  parts  in  two-cycle  motors  was  depicted 
previously,  also  the  function  of  the  valves  in  four-cycle  motors, 
the  function  of  the  valves  being  to  permit  the  entrance  and  escape 
of  the  gases  from  the  cylinders  at  the  proper  time.  These  valves 
are  termed  poppet  valves  and  consist  of  a  disc  of  metal  with  a 
stem  on  one  side,  which  closes  a  circular  opening  in  the  combus- 
tion chamber,  being  held  against  the  seat  in  the  wall  by  a  coiled 
wire  spring.  The  opening  and  closing  of  these  valves  is  by  a 
force  imparted  from  the  cam  shaft,  which  will  be  treated  later. 

Commercial  car  engines  of  the  poppet-valve  type  are  gener- 
ally classified  by  the  location  of  the  valves  within  the  cylinder, 
as  this  point  generally  controls  the  entire  construction  of  the 
motor,  as  well  as  the  various  factors  which  enter  into  its  design. 
The  various  types  of  cylinders  classified  by  their  valve  arrange- 
ments are  as  follows : 

T-Head. — A  type  in  which  all  valves  are  located  in  pockets  at 
opposite  sides  of  the  cylinders. 

L-Head. — A  type  in  which  all  valves  are  located  side  by  side 
in  one  pocket,  on  either  right  or  left  side  of  the  cylinder. 

Valve  in  Head. — A  type  in  which  all  valves  are  located  in  the 
cylinder  head,  placed  vertically  or  at  an  angle. 

There  are  also  several  other  types  which  are  combinations  of 
those  depicted  above,  having  one  valve  in  the  head  and  the  other 
in  a  pocket  at  the  side,  or  both  valves  in  a  pocket  at  the  side,  one 
being  located  above  the  other. 

The  first  and  second  types,  namely  the  T-head  and  the  L-head, 
are  by  far  the  most  popular  type  used  in  commercial  cars.  How- 
ever, quite  a  few  of  the  others  may  also  be  found.  The  first 
three  types  possess  an  advantage  in  that  all  working  parts  may 
be  inclosed  and  thoroughly  protected  from  grit.  They  also  pre- 
sent a  neater  appearance  in  that  it  is  a  simple  matter  to  keep 
them  clean,  as  all  parts  are  lubricated  internally. 

The  writer  is  presenting  several  illustrations  which  depict 
these  various  types  taken  from  illustrations  furnished  by  the 
various  makers  of  these  engines. 
3 


18      MOTOK  TRUCK  DESIGN  AND  CONSTRUCTION 


Fig.  13  depicts  the  conventional  type  of  T-head  cylinder  in 
which  all  the  intake  valves  are  located  on  the  right  side  and  all 

the  exhaust  valves  on  the  left 
side,  the  valves  being"  inserted 
through  openings  in  the  com- 
bustion chamber,  which  are 
covered  by  valve  port  plugs 
that  carry  the  spark  plugs. 

Fig.  14  depicts  the  conven- 
tional type  of  L-head  cylinder 
in  which  all  intake  and  exhaust 
valves  are  located  on  the  left 
side,  the  intake  and  exhaust 
valve  of  each  cylinder  being 
located  side  by  side  in  a  pocket. 
The  valves  have  conical  seats, 
as  those  depicted  in  Fig.  13, 
and  are  also  inserted  through 
FIG.  13.  Sectional  View  of  T-Head  openings  in  the  combustion 


chamber,  which  are  closed  by 
the    valve    port    plugs.      The 


Cylinder. 

plugs  which  cover  the  intake 
valve  openings  carry  the  spark 
plugs,  while  the  exhaust  port 
plugs  carry  the  relief  or  prim- 
ing cups.  In  this  motor  the 
valve  springs  are  of  conical 
shape,  the  object  of  this  being 
to  obtain  a  more  gradual  seat- 
ing of  the  valve.  The  valve 
stems  and  operating  parts  are 
also  enclosed;  however,  two 
aluminum  plates  are  used,  each 
covering  four  valve  stems. 
They  are  retained  by  a  wing 
nut  and  stud,  which  may  be 
quickly  removed. 

Fig.   15  depicts  a  valve  in 
the  head-type  cylinder  in  which 
the  valves  are  placed  vertical.    The  valve  stems  only  pass  through 
the  cylinder  and  for  this  reason  the  cylinder  is  divided  in  two 


FIG.  14. 


Sectional  View  of  L-IIead 
Cylinder. 


THE  MOTOR  TRUCK  ENGINE 


19 


parts  at  the  top  of  the  compression  space.  Valve  guides  are  used 
to  provide  a  bearing  for  the  valve  stems,  and  coil  wire  springs 
keep  the  valves  closed.  This 
construction  presents  an  ad- 
vantage in  that  the  entire 
compression  space  may  be  ma- 
chined to  a  polished  surface, 
thus  reducing  the  tendency 
for  carbon  to  collect  in  the 
combustion  chamber  and  di- 
viding the  cylinder  at  this 
point  also  facilitates  the  re- 
moval of  carbon  when  it  does 
form.  If  this  type  of  cylin- 
der were  cast  in  one  piece  it 
would  be  necessary  to  remove 
it  from  the  engine  in  order  to 
grind  the  valves,  unless  they 
were  mounted  in  cages  which 
could  be  removed. 

Fig.  11  depicts  one  type  of 
the  combination  of  types  and 
is  the  only  arrangement  re- 
sorted to  by  American  mak- 
ers, the  other  type  of  placing 
one  valve  over  the  other  has 
never  been  used  on  commer- 
cial car  motors  to  the  writer's 
knowledge,  the  combination 
in  this  type  being  identical 
with  the  construction  of  the 
other  types  from  which  they  were  derived,  one  valve  being  located 
in  a  p'ocket  and  operated  directly,  while  the  other  is  located  in  the 
head  and  is  carried  in  a  cage  in  the  cylinder  head  and  operated 
through  a  rocker  arm. 

During  the  past  year  there  has  been  a  tendency  to  divide 
L-head  cylinders  of  the  motor  used  in  light  delivery  wagons,  so 
that  part  of  the  crank  case  could  be  cast  integral  with  the  cylin- 
ders. This  construction,  of  course,  presents  advantages  in  the 
removal  of  carbon,  valve  grinding,  finishing  of  the  combustion 
space,  as  well  as  reducing  the  cost  of  manufacture.  It  remains, 


FIG.  15.     Sectional   view    of   Valve- 
in-Head  Cylinder. 


20   MOTOE  TRUCK  DESIGN  AND  CONSTRUCTION 

however,  to  be  seen  just  what  popularity  this  construction  will 
gain  in  the  heavier  types  of  motors. 

There  are  various  ways  of  grouping  cylinders,  as  they  may 
either  be  cast  single,  in  pairs  or  en  bloc.  Where  they  are  cast 
single  the  motor  becomes  of  considerable  length  and,  of  course, 
requires  a  much  longer  hood;  this  additional  space  when  added 
to  the  loading  compartment  would  naturally  be  of  considerable 
advantage.  Casting  them  in  pairs  shortens  the  motor  somewhat. 
However,  the  ideal  construction  is  obtained  when  the  cylinders 
are  cast  en  bloc,  which  permits  of  the  shortest  possible  hood 
length.  It  also  presents  an  advantage  in  the  shorter  length  of  the 
vital  parts  such  as  the  crank  and  cam  shaft,  crank  case,  etc.,  as 
the  space  wasted  can  be  put  to  good  advantage  by  the  increasing 
of  the  main  bearings  and  the  shortening  of  the  unsupported  parts 
of  these  shafts. 

This  method  of  cylinder  grouping  can  be  applied  to  any  type 
of  motor,  or  valve  arrangement,  and  is  not  dependent  upon  any 
one  construction.  En  bloc  cylinder  construction  does  present  a 
very  simple  and  neat  motor,  especially  when  all  parts  are  properly 
enclosed. 

The  Valve  Operating  Mechanism  and  the  Crank  Case. — Hav- 
ing described  the  functions  of  the  valves  in  their  respective  cyl- 
inders, we  can  next  consider  how  their  operation  is  accomplished, 
at  the  proper  time,  by  mechanical  connection  with  the  crankshaft. 

Functions  of  the  Cams  and  Cam  Shaft. — This  is  accomplished 
by  cams  which  are  attached  to,  or  formed  integral  with,  a  shaft 
termed  the  "camshaft,"  which  in  turn  is  driven  through  a  gear, 
which  meshes  with  an  idler  gear,  or  with  the  crankshaft  gear. 
When  an  idler  or  intermediate  gear  is  used  it  is  so  placed  that  it 
will  mesh  with  both  the  crankshaft  and  camshaft  gears.  It  is 
only  used  when  the  latter  gears  cannot  be  meshed  directly,  due  to 
the  difference  in  centers  between  cylinders  and  valves  and  the  two 
shafts. 

The  camshaft  is  so  designed  that  the  rise  of  the  cam  is  brought 
into  operation  at  the  proper  time,  causing  the  valve  to  be  raised 
from  its  seat  and  to  permit  a  charge  to  enter  or  escape  from  the 
cylinder.  This  cam  only  causes  the  valve  to  raise  from  its  seat; 
in  other  words,  causes  the  valve  to  open,  while  the  valve  spring 
performs  the  function  of  closing  it  and  holding  it  down  on  its 
seat  until  the  cam  again  opens  the  valve.  In  the  discussion  of  the 
two  and  four-cycle  motors  it  was  pointed  out  that  one  valve 
opens  during  each  revolution  of  the  crankshaft,  the  valves  alter- 


THE  MOTOR  TRUCK  ENGINE         21 

nating,  first  one  and  then  the  other.  From  this  it  can  readily  be 
understood  that  the  camshaft  must  revolve  at  one-half  of  the 
crankshaft  speed,  thus  necessitating  a  two  to  one  reduction  in  the 
timing  gears. 

In  this  case  we  also  have  to  convert  a  rotary  motion  into  a 
reciprocating  motion.  However,  as  no  permanent  connection  is 
made  with  the  camshaft,  this  becomes  a  simple  matter  by  provid- 
ing what  is  termed  the  pushrod,  one  end  of  which  communicates 
with  the  valve  stem  and  other  end  rests  on  the  cam.  It  is  pro- 
vided with  a  suitable  bearing  so  that  its  relation  with  the  cam- 
shaft can  always  be  maintained. 

These  pushrod^  may  either  have  the  bearing  or  guide  in  the 
crank  case  or  in  the  base  of  the  cylinders.  When  the  valve  stems 
are  enclosed  it  is  more  advantageous  to  place  them  in  the  cyl- 
inders, as  it  somewhat  simplifies  the  machining  operations  of  the 
case  and  also  the  assembling  of  the  motor.  These  pushrods  are 
always  provided  with  adjusting  screws,  so  that  as  little  lost  motion 
as  is  practical  may  be  present  between  the  valve  stem  and  the 
cam.  This  feature  can  also  be  maintained  through  these  screws 
which  are  locked  in  position  by  lock  washers  and  nuts. 

All  T-head  motors  require  two  camshafts,  while  the  balance 
of  the  types  illustrated  require  but  one  shaft,  as  all  valves  can  be 
operated  from  one  side  of  the  motor.  Two  camshafts  could  be 
used  in  the  other  types,  excepting  the  L-head,  but  this  of  course 
would  add  complications  in  the  motor.  The  train  of  gears  for 
operating  the  valve  and  the  accessories  is  dependent  upon  the 
number  of  shafts  and  the  general  distribution  of  the  accessories. 
They  are  generally  provided  with  helical  teeth  and  located  in  a 
housing  at  the  forward  end  of  the  crank  case.  They  must  be  com- 
pletely enclosed  so  that  they  may  be  effectively  lubricated  and 
protected  from  dust.  This  housing  is  generally  built  into  the 
case  and  provided  with  a  cover  plate. 

The  Crank  Case. — The  crank  case,  as  mentioned  in  the  pre- 
vious installment,  serves  as  the  main  structural  part  of  the  motor, 
carrying  the  cylinders,  crankshaft,  camshaft  and  accessories,  and 
is  in  turn  supported  in  the  vehicle  frame.  It  also  forms  a  hous- 
ing for  these  important  parts,  protecting  them  against  dust  and 
mud,  and  also  performs  important  functions  in  connection  with 
the  lubrication  of  the  motor.  The  crank  case  generally  forms 
either  a  cylindrical  or  box-shaped  housing  of  sufficient  size  to 
enable  the  crank  pins  with  their  respective  connecting  rods  to 


22      MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

rotate  freely  within  it  and  sufficiently  long  to  accommodate  all  of 
the  cylinders  of  the  motor,  which  are  bolted  over  the  opening  in 
the  top  of  the  case. 

The  general  design  of  this  case  depends,  of  course,  upon  the 
number  of  cylinders,  the  valve  location  and  the  size  of  the  crank- 
shaft and  its  bearings. 

There  are  various  methods  of  mounting  the  motor  in  the 
vehicle  frame,  each  having  its  advantages  and  disadvantages. 
The  case  is  generally  provided  with  four  arms,  which  may  either 
be  cast  integral  or  bolted  to  it,  when  main  frame  mounting  is  re- 
sorted to,  while  for  sub-frame  mounting  they  are  always  cast 
integral. 

Lately  there  has  been  quite  a  tendency  toward  the  use  of  a 
three-point  support  for  the  motor  so  as  to  eliminate  stresses  in 
the  case,  due  to  frame  weaving  from  road  irregularities.  This 
type  of  motor  support  may  either  be  incorporated  in  the  motor, 
by  using  a  separate  arm  pivoting  around  the  crankshaft  center  at 
either  the  front  or  rear  end,  when  main  frame  mounting  is  re- 
sorted to  and  by  incorporating  this  support  at  either  the  front  or 
rear  end  of  the  sub-frame  when  the  latter  mounting  is  used. 

Crank  cases  may  either  be  formed  in  one  piece  with  a  separate 
oil  reservoir  or  in  two  pieces  divided  on  the  horizontal  center  of 
the  crankshaft.  They  may  either  be  cast  iron  or  aluminum  and 
in  several  instances  manganese  bronze  has  been  used.  Aluminum 
is  the  most  popular,  provided  with  separate  steel  supporting 
arms  which  are  bolted  to  the  case,  owing  to  the  heavy  vibrations 
due  to  the  solid  tires. 

Unit  Power  Plants. — Quite  a  few  of  the  commercial  vehicles 
use  the  unit  powrer  plant  in  which  the  gear  box  or  transmission  is 
bolted  directly  to  a  housing  cast  integral  with  the  case  and  sur- 
rounding the  flywheel,  or  by  separate  arms  which  are  bolted  to 
the  rear  motor  arms.  However  this  method  is  very  rarely  re- 
sorted to  in  the  heavier  types  owing  to  the  large  size  of  the  trans- 
mission, its  weight  and  the  necessity  of  providing  a  separate  jack- 
shaft  for  chain  driven  vehicles. 

Like  all  other  units  of  the  commercial  car,  there  are  various 
designs  which  have  been  worked  out  and  giving  excellent  results, 
and  the  writer  presents  illustrations  of  the  types  conforming  to 
the  general  outline  of  the  motors  referred  to. 

The  writer  will  not  endeavor  to  describe  the  various  methods 
of  mounting  the  engine  in  the  vehicle  frame,  as  this  can  be  done 


THE  MOTOR  TRUCK  ENGINE 


23 


more  clearly  by  devoting  a  chapter  to  this  feature  which  will 
cover  all  of  the  present  methods  pertaining  to  all  units  mounted 
in  the  frame. 


COYER 
PLATE 


BEARIN 


CAM  SHAF 


CRANK  SHAFT    ^ 
FIG.  16.     Showing  Valve  Mechanism  of  L-IIead  Motor. 

Fig.  16  shows  the  valve  operating  mechanism  used  on  a  promi- 
nent L-head  commercial  car  motor,  illustrating  how  the  valves 
are  located  side  by  side.  The  European  type  of  valve,  with  con- 
ical seat  and  the  most  popular  method  of  enclosing  the  valves  to 
protect  them  from  dust  and  foreign  matter,  are  shown.  The 
pushrod  guides  are  pressed  into  the  cylinder  and  can  readily  be 
removed  from  the  bottom  of  the  same.  When  the  cylinder  is  re- 
moved from  the  crank  case  the  entire  valve  mechanism,  excepting 
the  cams  and  their  shaft,  is  removed  with  the  cylinder,  a  note- 
worthy feature  when  the  overhauling  of  an  engine  is  considered. 
The  pushrod  is  of  the  mushroom  type  and  the  outline  of  the  cam 
is  formed  of  curves,  to  further  assist  in  obtaining  a  quieter  valve 
action.  The  conventional  type  of  pushrod  adjustment  incorpo- 


24      MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


FIG.  17.  Showing  the 
Method  of  Operating 
Valve  when  Located  in 
Cylinder  Head. 


rating  a  hardened  steel  screw  and  lock  nut  is  used.  This  view 
also  shows  the  large  bearing  provided  for  the  cam  shaft  so  that 
it  may  be  removed  through  the  forward  end  of  the  case.  Helical 

teeth  are  used  on  the  timing 
gears  and  the  end  thrust  is 
taken  by  a  hardened  steel 
pin  supported  by  a  spring 
which  transmits  this  thrust 
to  hardened  steel  washer  on 
the  timing  gear  housing 
cover. 

Fig.  17  illustrates  the 
method  of  operating  the 
valves  when  they  are  located 
side  by  side  in  the  cylinder 
head.  The  pushrods  are 
similar  to  those  previously 
described  above,  however, 
the  adjustment  is  omitted 
here  and  incorporated  with 
the  rocker  arm  mounted  on 

top  of  the  cylinder.  These  rocker  arms  pivot  on  a 
shaft  and  their  opposite  ends  bear  against  the  valve 
stems.  The  operating  rod  placed  between  the  push- 
rod  and  the  adjustment  in  the  rocker  arm  has  a  ball- 
shaped  end  to  reduce  wear  at  this  point. 

Fig.  18  illustrates  the  overhead  type  of  valve  me- 
chanism for  valve  in  the  head  cylinders  with  valves 
set  at  an  angle  on  opposite  sides  and  operated  through 
one  camshaft  located  on  the  cylinder  heads.  It  will 
be  noticed  that  a  very  light  spring  is  used  for  the  in- 
take valve,  while  a  very  stiff  spring  is  used  for  the 
exhaust  valve.  The  object  being  to  make  the  intake 
valve  partly  automatic,  owing  to  the  fact  that  but 
one  rocker  arm  is  used  to  operate  both  valves.  The 
rocker  arm  of  course  replaces  the  pushrods  and  the 
adjustment  is  incorporated  in  the  ends  of  the  arms. 
The  rocker  arm  has  a  roller  bearing  'against  the  cam,  and  these 
two  parts  are  kept  in  contact  by  a  large  spiral  spring.  The  cam- 
shaft bearings  are  divided,  but  require  considerable  attention,  as 
a  wick  feed  is  resorted  to  for  supplying  lubricant.  The  cam, 


THE  MOTOR  TRUCK  ENGINE 


25 


roller  and  other  parts  are  exposed  so  that  grit  and  foreign  matter 
can  reach  them,  and  it  is  a  contraction  very  hard  to  lubricate 
due  to  the  intense  heat  on  the  cylinder  heads. 


FIG.  18.     Overhead  Type  of  Valve  Mechanism.     Valves  set  at  an  Angle. 

The  combination  type  of  valve  arrangement  of  course  em- 
bodies the  features  of  those  just  described.  Fig.  16  can  be  ap- 
plied to  the  valve  in  the  pocket,  while  Fig.  17  would  apply  to  the 
valve  in  the  head  or  in  the  pocket  when  these  are  placed  one  above 
the  other. 

Various  methods  are  resorted  to  in  fastening  the  pushrod 
guides  into  the  cylinders  or  case.  They  may  either  be  pressed  in 
position,  held  down  in  pairs  by  clamps  or  bolted  down. 


26   MOTOE  TRUCK  DESIGN  AND  CONSTRUCTION 


These  various  constructions  may  be  applied  to  most  any  valve 
location.  The  principal  change  would  come  in  the  crank  case, 
which  is  dependent  upon  the  number  of  camshafts  that  are  neces- 
sary to  operate  the  valves.  Enclosing  the  valve  stems  and  push- 
rods  is  now  quite  popular. 

Fig.  19  illustrates  a  bottom  view  of  a  T-head  crank  case  in 
which  the  two  camshafts  with  the  respective  parts  are  clearly 
shown.  This  view  also  shows  a  three-bearing  crankshaft  with 


CAM 
SHAFT 


CAM 

SHAFT 


OIL  PUMP 


FIG.  19.     Bottom  View  of  a  T-Head  Crank  Case,  Showing  two  Cam  Shafts. 

the  connecting  rods  fastened  in  position  on  the  shaft  and  in  the 
piston.  The  case  is  divided  and  all  bearings  are  held  in  position 
by  separate  caps,  while  the  cams  are  of  considerable  width,  as  the 
exhaust  camshaft  can  be  moved  longitudinally  so  as  to  provide  a 
compression  release  for  cranking  the  motor.  This  is  accom- 
plished through  the  use  of  stepped  exhaust  cams  which  open  the 
exhaust  valve  part  way  during  a  portion  of  the  compression 
stroke  while  cranking  the  motor.  The  water  pump  is  located  at 
the  front  end  of  the  motor  and  is  driven  through  separate  gears 
meshing  with  camshaft  gears.  The  oil  pump  is  located  on  the 
rear  motor  arm  and  is  driven  through  a  ratchet  and  link  connec- 
tion with  a  valve  pushrod. 


THE  MOTOR  TRUCK  ENGINE 


27 


Fig.  20  illustrates  a  bottom  view  of  a  crank  case  for  the  L-head 
motor.  It  shows  the  camshaft  and  crankshaft  in  position,  with 
the  connecting  rods  mounted  on  the  crank  pins.  But  one  cam- 


FIG.  20.     Bottom   of    Crank   Case   of   L-Head   Motor. 

shaft  is  used,  and  is  driven  through  helical  gears,  the  accessories 
are  mounted  on  opposite  sides  and  also  driven  through  helical 
gears.  The  crankshaft  is  of  the  five-bearing  type,  while  the  case 


FIG.  21.     Bottom  View  of  Crank  Case  having  Separate  Compartment 

for  Oil. 

is  divided  on  the  horizontal  center  of  the  crankshaft,  all  the  im- 
portant parts  being  carried  in  this  upper  half  of  the  case,  the 


28      MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


lower  half  serving  only  as  a  dust  protection,  oil  splash  basin  and 
reservoir. 

Fig.  21  illustrates  the  bottom  view  of  a  prominent  valve  in 
the  head  motor,  with  a  three-bearing  crankshaft  and  one  cam- 
shaft for  operating  the  valves.  This  crank  case  differs  somewhat 
from  the  above  in  that  it  is  cast  in  one  piece  with  a  separate  oil 
reservoir  bolted  to  it.  The  timing  gears  are  carried  in  a  housing 
at  the  front  end  of  the  case,  enclosed  by  a  .steel  cover  plate.  The 
magneto  is  driven  from  the  timing  gear  housing  through  flexible 
couplings  in  the  conventional  way,  while  the  pump  is  driven 
through  spiral  gears  from  the  camshaft. 


TIMING  6EAR 
CAM 

ROLLER   TYPE 
PUSH    ROD 


ILtYLINOER 


FLY 

WHEEL 


CRANK 
SHAFT 


CRANK  CASE 
OIL  RESERVOIR 
OIL  F»UMF 


FIG.  22.     Sectional    View    of    Two    Cylinder    Opposed    Motor. 

Fig.  22  shows  a  sectional  view  of  a  two-cylinder  opposed 
motor.  This  type  of  motor  is  mostly  used  on  the  light  commer- 
cial vehicles,  and  the  case  is  generally  made  from  cast  iron.  This 
case  is  cast  in  one  piece  with  circular  openings  on  the  ends, 
through  which  the  crankshaft  is  inserted.  Plates  are  mounted 
in  these  openings  and  bolted  to  the  case  which  carries  the  crank- 
shaft bearings.  A  large  cover  plate  is  used,  which  carries  the 
camshaft,  gears  and  pushrods.  The  water  pump  is  driven  by  the 
camshaft  bevel  gears,  while  the  oil  pump  is  driven  through  an 
idler  gear  from  the  crankshaft. 


THE  MOTOR  TRUCK  ENGINE         29 

In  some  of  the  two-cylinder  motors  in  use  at  present  the  case 
is  divided  on  the  vertical  center  of  the  crankshaft  and  each  half 
is  cast  integral  with  a  cylinder,  while  the  pushrods  and  cam- 
shafts are  also  located  in  the  case  instead  of  on  the  cover  plate. 

In  the  two-cylinder  opposed  type  of  motor  the  distance  be- 
tween the  crankshaft  and  the  camshaft  is  generally  greater  than 
the  distance  between  the  valve  and  the  cylinder  centers.  This  is 
due  to  the  fact  that  in  this  type  of  motor  the  camshaft  is  located 
at  right  angles  to  the  cylinder  axis,  while  in  the  vertical  motors 
it  generally  makes  an  angle  of  45  to  60  degrees  with  the  cylinder 
axis.  The  former  case  makes  it  necessary  to  either  place  the  valve 
chamber  farther  from  the  cylinder  axis,  thereby  increasing  the 
length  of  the  valve  passage  and  consequently  the  compression 
space  wall  area,  which  is  not  good  practice,  or  to  offset  the  valves 
from  the  camshaft  center  and  to  provide  the  pushrods  with  an 
overhanging  striker.  In  Fig.  22  the  pushrods  are  set  at  an  angle 
to  overcome  this  point,  which  in  this  case  is  easily  accomplished, 
as  the  valves  are  carried  in  the  head  of  the  cylinder  and  operated 
through  a  rocker  arm. 

Motor  Lubrication. — Developments  in  the  line  of  motor  lubri- 
cation as  a  matter  of  course  follow  on  the  heels  of  progress  in  the 
art  of  motor  design  and  construction,  for  the  increase  of  efficiency 
which  marks  the  refinement  of  the  motor  and  its  various  parts 
can  only  be  reached  if  the  refinements  are  paralleled  by  those 
essentials  which  permits  the  units  to  perform  their  required  duty. 
In  commercial  car  motors,  the  two  features,  outside  of  actual 
mechanical  construction  and  the  essential  details  of  ignition  and 
carburetion,  which  help  to  the  attainment  of  the  highest  results 
with  the  least  expenditure  are  the  cooling  and  lubricating  systems. 

The  functions  of  the  cooling  system  are  different  from  those 
of  the  lubricating  system  and  will  be  considered  in  a  separate 
article  following  the  present  one. 

All  parts  which  rub  together  under  pressure,  such  as  the  pis- 
tons moving  upward  and  downward  within  the  cylinders,  the 
connecting  rods  on  the  piston  and  crank  pins,  the  crank  shaft  in 
its  bearings  and  all  reciprocating  and  revolving  parts  must  be 
efficiently  lubricated.  Whenever  two  surfaces  are  in  contact  and 
one  or  other  is  free  to  move  when  a  force  is  applied,  there  is  pres- 
ent a  certain  amount  of  friction,  which  develops  instantly  when 
these  surfaces  are  not  properly  lubricated. 

Friction  is  a  resistance  to  motion  of  two  bodies  in  contact  and 


30      MOTOE  TKUCK  DESIGN  AND  CONSTRUCTION 

is  dependent  upon  certain  laws.  It  will  vary  in  proportion  to  the 
pressure  applied  when  the  rubbing  velocity  remains  constant. 
All  wearing  surfaces,  no  matter  how  carefully  prepared,  are 
known  to  consist  of  minute  lumps  and  hollows.  This  is  true,  even 
of  the  smoothest  surfaces  that  can  be  made,  although,  of  course, 
the  height  of  the  depressions  and  hollows  varies  with  different 
materials  and  the  finish.  The  condition  of  bearing  surfaces  in 
an  exaggerated  degree  may  be  likened  to  the  nap  of  woolen  cloth 
and  the  pile  of  velvet. 

When  the  two  surfaces  are  held  in  contact  by  an  appreciable 
force  these  minute  parts  of  the  surfaces  interlock  and  resist  rela- 
tive motion.  This  force  is  called  the  force  of  friction.  This  fact 
can  easily  be  demonstrated  by  placing  a  book  upon  a  table  or 
smooth  board  and  moving  it  across  the  latter,  comparing  the  dif- 
ference in  energy  required  to  move  the  book  across  the  surface 
by  placing  a  weight  upon  it.  If  this  experiment  were  conducted 
with  two  metallic  objects  and  the  surfaces  were  lubricated,  con- 
siderable less  energy  would  be  required. 

Friction  in  reality  is  heat,  which  in  a  short  period  of  time  will 
reach  an  intense  degree  and  in  time  the  surfaces  will  be  broken 
down  and  if  the  rubbing  continues  they  will  be  completely  de- 
stroyed. The  action  and  effect  of  this  friction  upon  two  surfaces 
not  properly  lubricated  may  be  explained  as  follows:  At  first 
small  particles  of  metal  are  torn  from  the  surfaces  and  these  cut 
and  abrade  the  bearing.  As  the  surfaces  continue  to  roughen, 
the  friction  increases  enormously  until  it  reaches  the  fusing  point 
of  the  metal,  when  the  two  surfaces  will  weld  into  one  solid  mass. 

A  lubricant  should  possess  certain  qualities,  since  its  object  is 
to  flow  between  the  surface  of  a  bearing,  reduce  its  friction  and 
to  radiate  a  certain  amount  of  heat  generated  by  the  bearing. 
These  properties  are  termed  adhesion,  cohesion  or  viscosity,  a 
high  flash  point  and  a  comparatively  low  cold  test  point.  It 
should  have  considerable  adhesion  so  that  the  molecules  of  oil 
will  cling  together,  considerable  cohesion  or  viscosity,  as  all  bear- 
ings are  subjected  to  a  pressure,  created  by  the  force  acting  upon 
them  and  the  effect  of  this  pressure  is  a  tendency  to  separate 
these  molecules  forcing  sufficient  lubricant  out  of  the  bearing  to 
allow  the  metals  to  come  into  contact. 

The  advantage  of  a  high  flash  point  is  that  the  oil  will  not 
give  off  an  inflammable  vapor  at  ordinary  temperature,  while  it 
should  have  a  low  cold  test  point,  so  that  it  will  stay  in  fluid  state 
when  cold  temperature  are  encountered.  The  high  flash  point  is 


THE  MOTOR  TRUCK  ENGINE         31 

very  desirable;  for  in  lubricating  the  cylinders,  the  oil  comes  in 
contact  with  the  walls  of  the  combustion  chamber  and  the  heat  in 
the  cylinder  on  the  power  stroke.  If  the  temperature  is  raised 
sufficiently  to  vaporize  the  oil,  the  viscosity  is  entirely  overcome 
and  the  various  residue  products  of  the  lubricant  are  deposited 
on  the  walls  of  the  combustion  chamber.  This  residue  product  is 
termed  carbon  and  in  time  will  harden,  become  incandescent  and 
fire  the  charge  prematurely,  causing  excessive  strains  on  the 
various  parts  of  the  motor.  The  final  result  is  that  the  motor  will 
begin  to  pound,  overheat  very  easily,  the  valves  will  pit  and  the 
spark  plugs  become  fouled. 

The  advantage  of  a  low  cold  test  point  is  that  it  will  flow 
freely  in  cold  weather,  preventing  the  oil  leads  and  pump  from 
clogging  up. 

There  are  various  methods  of  lubricating  the  working  parts 
of  commercial  car  engines,  and  it  is  a  difficult  matter  to  classify 
them.  We  may  distinguish,  however,  between  the  following: 
Plain  splash;  splash  from  constant  level  troughs  with  pump  cir- 
culation; part  force  feed  and  part  splash;  force  feed  without 
splash ;  either  from  an  external  source  or  built  into  the  motor. 

The  simple  splash  system  was  much  used  on  the  earlier  models 
of  commercial  cars.  The  crank  case  contained  a  supply  of  oil 
into  which  the  connecting  rods  dipped  at  each  revolution  of  the 
crank  pin,  thereby  splashing  oil  over  the  interior  parts.  As  the 
oil  worked  out  through  the  bearings  or  past  the  pistons,  the  oil 
level  in  the  crank  case  fell  and  the  splash  became  weaker.  When 
the  operator  considered  that  the  oil  level  had  become  too  low,  he 
would  replenish  the  supply  by  either  pouring  oil  into  the  crank 
case  through  a  filling  hole  or  transferring  it  from  a  supply  tank 
to  the  crank  chamber  by  means  of  a  hand  pump  provided  for  the 
purpose. 

The  disadvantages  of  this  system  are  apparent.  The  oil  level 
varied  constantly  and  so  did  the  rate  of  supply  to  the  bearing 
surfaces.  When  the  crank  case  was  replenished,  the  oil  level  was 
raised  considerably  and  the  supply  to  cylinder  walls  was  generally 
excessive  and  the  motor,  in  consequence,  would  pour  dense  smoke 
out  through  the  muffler.  In  order  to  overcome  this  feature,  some 
makers  placed  baffle  plates  between  the  cylinder  and  the  crank 
case  with  an  opening  in  the  form  of  a  rectangular  slot  for  the 
connecting  rod  to  pass  through.  Moreover  this  system  required 
frequent  attention  from  the  operator,  and  if  the  latter  were  care- 
less, the  motor  could  easily  be  injured  through  the  lack  of  oil. 


32      MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

Through  the  deficiencies  mentioned  above,  lubrication  by 
multiple  feed  mechanical  oilers  came  into  vogue.  These  oilers 
consisted  of  an  oil  reservoir  carrying  a  series  of  plunger  pumps, 
which  forced  the  oil  through  individual  leads  to  each  part  re- 
quiring lubrication.  Each  lead  had  its  own  pump,  so  that  the  oil 
was  forced  to  each  bearing  in  proportion  to  the  speed  of  the 
motor.  While  this  system  was  effective,  its  complications  were 
objectionable.  It  was  difficult  to  obtain  a  positive  drive  and  the 
maze  of  oil  tubes  running  from  the  oiler  to  the  engine,  rendered 
access  to  the  latter  difficult  and  presented  a  frail  and  non-mechan- 
ical appearance.  It  was  also  difficult  to  prevent  leaks  at  the 
various  connections  and  considerable  oil  was  wasted. 

Following  this  the  pump  circulating  systems  were  introduced, 
as  it  was  felt  that  a  simpler  system  was  needed  and  one  that  was 
at  the  same  time  thoroughly  automatic.  The  gear  and  plunger 
types  of  oil  pumps  are  most  popular ;  however  in  some  cases  vane 
pumps  are  also  used. 

The  gear  pump  consists  of  a  casing  in  which  fit  snugly  two 
spur  gears,  one  driven  by  means  of  its  shaft  and  gears  from  the 
cam  shaft  and  the  other  by  meshing  with  the  former.  The  oil 
enters  the  housing  on  the  side  on  which  the  meshing  teeth  separate 
and  fills  the  spaces  between  adjacent  teeth  and  the  wall  of  the 
housing.  It  is  thus  carried  around  to  the  opposite  side  of  the 
housing  and  leaves  through  an  opening  there. 

Plunger  pumps  are  generally  placed  inside  the  crank  case  and 
driven  by  eccentrics  from  the  cam  shaft.  They  consist  of  a  brass 
barrel  set  in  the  case  and  carrying  a  plunger,  which  is  held  in 

contact  with  the  eccentric 
by  a  spring.  .Below  the 
spring  a  ball  valve  is 
placed.  As  the  plunger 
moves  upward,  the  lower 
end  of  the  barrel  increases 
in  volume  and  oil  enters 
through  the  ball  valve. 
When  the  plunger  is  next 
moved  down  by  the  eccen- 

FIG.  23.     Exterior  of  a  Mechanical  Oiler.       trie,   the   ball   valve   closes 

and     oil     is     forced     up 

through  and  out  another  ball  valve,  which  remains  closed  on  the 
upward  stroke  of  the  plunger. 


THE  MOTOE  TKUCK  ENGINE 


33 


In  what  follows  the  writer  will  attempt  to  describe  and  illus- 
trate the  most  popular  systems  in  use  at  present,  among  which 
both  the  gear  and  plunger  types  of  pumps  will  be  found. 

Fig.  23  shows  a  mechanical  oiler  which  operates  in  the  follow- 
ing manner.  A  series  of  double  plunger  valveless  pumps  are 
driven  by  belt  from  a  cross  shaft  which  is  driven  by  the  engine. 
One  set  of  plunger  pumps  lift  oil  from  the  reservoir  and  dis- 
charge it  from  the  nozzles  in  the  sight  feed  compartment,  the 
amount  of  oil  discharged  being  regulated  by  the  adjusting  screws 
A,  directly  in  front  of  the  sight  feed.  The  other  set  of  plungers 
take  oil  from  the  sight  feed  compartments  and  deliver  it  to  the 
various  parts  of  the  engine  through  the  oil  lead  connected  with 
the  pump  outlet  B.  The  plungers  work  alternately  and  each  acts 
on  a  check  valve  for  the  other. 


FIG.  24.     Recirculating1  Splash  System  of  Lubrication. 

Fig.  24  illustrates  a  circulating  splash  system  which  has  been 
used  for  a  number  of  years  on  a  prominent  motor.  Two  plunger 
pumps  are  located  in  the  lower  half  of  the  case  and  driven  by 
eccentric  from  the  cam  shaft.  One  pump  supplies  oil  to  the 
timing  gear  compartment,  and  from  these  points  it  overflows  to 
the  splash  troughs  cast  integral  with  the  case. 

The  connecting  rods  are  provided  with  dippers  which  are 
hollow  and  permit  a  certain  amount  of  oil  to  reach  the  connect- 
ing rod  bearings  during  each  revolution  of  the  crank  pin.  They 
also  splash  oil  over  the  interior  parts  of  the  motor,  the  crank 
and  cam  shaft  bearing  housings  being  provided  with  pockets 
which  store  the  oil  and  feed  it  to  the  bearings  as  it  is  needed. 
4 


34      MOTOE  TEUCK  DESIGN  AND  CONSTEUCTION 


Each  connecting  rod  has  a  separate  trough  into  which  it  dips, 
and  the  two  forward  ones  are  separated  from  the  rear  by  a  high 

partition,  so  that  a  positive 
oil  level  can  be  maintained 
for  all  conditions,  when 
traveling  up  or  down 
grade. 

Fig.  25  shows  another 
constant  level  splash  sys- 
tem of  the  recirculating 
type.  The  operation  of  the 
system  is  similar  to  the  one 
explained  above,  oil  being 
supplied  to  the  stationary 
troughs  by  a  gear  pump. 
Scoops  on  the  connecting 
rods  dip  into  these  troughs 

FIG.  25.  Base  Removed  on  Constant-  and  cause  the  oil  to  sPlash 
Level  Splash  Lubricated  Motor.  onto  the  pistons  and  into 

the  small  reservoirs  which 

lead  to  the  various  bearings.  The  surplus  oil  drains  back  to  the 
main  reservoir,  when  it  is  thoroughly  strained  and  again  recir- 
culated. 

Fig.  26  illustrates  a  gravity-feed  system  using  a  gear  pump 
for  supplying  oil  to  the  gravity  tank  from  the  reservoir  in  the 
lower  half  of  the  case.  This  gravity  tank  is  placed  at  the  top 
level  of  the  cylinders  and  has  an  oil  lead  of  large  diameter  to 
each  of  the  main  bearings  and  the  timing-gear  compartment. 
The  delivery  pipe  and  leads  are  provided  with  strainers,  so  that 
the  oil  is  thoroughly  strained  before  being  recirculated.  The 
crank  shaft  journals  and  short  arms  are  drilled  through,  so  that 
the  oil  can  pass  from  the  main  bearings  to  the  connecting  rods, 
centrifugal  force  being  relied  on  to  carry  this  oil  to  the  connect- 
ing rods.  Part  of  this  oil  works  through  these  bearings  and 
creates  a  spray,  as  in  the  force-feed  system.  This  spray  lubricates 
all  other  moving  parts.  It  will  be  noted  that  the  shape  of  the  oil 
tank  is  such  that  when  the  car  is  moving  up  or  down  grade  all 
bearings  will  receive  an  equal  amount  of  oil.  An  oil  gage  on  the 
dash  shows  the  amount  of  oil  in  the  tank,  indicating  that  the 
pump  is  doing  its  work. 

Fig.  27  illustrates  a  sectional  view  of  a  full  force  feed  system 
of  lubrication  which  is  built  into  the  motor.  Oil  is  carried  in  a 


THE  MOTOR  TRUCK  ENGINE 


35 


reservoir  bolted  to  the  crank  case  and  is  circulated  by  a  gear 
pump  mounted  at  the  rear  end  of  the  case  driven  from  the  cam 
shaft.  The  pump  forces  oil  up  through  a  pipe  over  the  main 
bearings  and  is  provided  with  a  pressure  relief  valve.  This  dis- 


HAN  Or  OH.  PUMP 

FIG.  26     Combination  Pump  and  Gravity  System. 

tributing  pipe  has  branches  which  communicate  with  the  main 
bearings  and  the  timing  gears.  From  the  main  bearings  the  oil 
is  forced  through  a  hollow  crank  shaft  to  the  connecting  rod 
bearings.  These  connecting  rods  have  tubes  inserted  in  them  so 
that  the  oil  can  be  forced  up  to  the  piston  pin  bearings.  Cam 
shaft  bearings  are  lubricated  by  means  of  passages  connected  with 
the  system.  A  certain  portion  of  the  oil  works  out  from  the  con- 
necting rod  bearings,  is  thrown  off  as  the  crank  shaft  revolves 


36      MOTOE  TKUCK  DESIGN  AND  CONSTRUCTION 

and  forms  a  fine  spray  which  lubricates  the  cylinders,  pistons  and 
interior  parts  of  the  motor.  An  indicator  which  shows  at  all 
times  the  level  of  oil  in  the  reservoir  is  placed  adjoining  the  com- 
bination breather  and  filling  tube.  The  oil  pump  and  its  strainers 
are  removable  from  the  lower  half  of  the  crank  case  without  dis- 


FIG.  27.     Full  Force  Feed  Lubricating  System. 

turbing  other  parts.  The  pressure  relief  valve  permits  a  certain 
oil  pressure  on  the  bearings.  Should  the  pressure  exceed  this 
predetermined  amount  the  relief  valve  will  open,  permitting  the 
excess  oil  to  return  to  the  reservoir.  Oil  which  overflows  and 
accumulates  in  the  case  flows  into  a  trough  into  which  the  con- 
necting rods  dip.  This  trough  has  holes  on  one  side  which  allow 
the  oil  to  drain  back  to  the  reservoir  beneath  so  that  a  constant 
level  of  oil  is  maintained. 

Fig.  28  illustrates  the  Mack  oiling  system  which  is  a  com- 
bination of  the  gravity  and  force  feed  type.  Oil  is  pumped  from 
the  reservoir  at  the  bottom  of  the  crank  to  a  tank  cast  integral 
with  the  front  pair  of  cylinders.  This  tank  is  provided  with  a 
filter  and  an  overlow  which  leads  to  the  timing  gear  housing. 
This  tank  serves  two  functions:  first,  to  heat  the  oil  while  the 


38      MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

engine  is  cold  so  that  the  oil  will  flow  freely  and  second,  to  cool 
the  oil  when  the  engine  is  working  hardest,  as  the  oil  may  reach 
a  temperature  of  390  degrees  Fahrenheit,  while  the  cooling  sys- 
tem seldom  reaches  a  temperature  higher  than  190  degrees 
Fahrenheit.  From  the  tank  the  oil  flows  to  a  main  header  which 
supplies  oil  to  the  main  bearings  and  through  a  second  header 
which  supplies  oil  to  the  troughs  into  which  the  connecting  rods 
dip.  A  pressure  gauge  is  used  to  indicate  the  oil  pressure  and 
the  pump  is  provided  with  a  strainer  to  filter  the  oil  before  it  is 
recirculated. 

The  constant  level  splash  and  force  feed  systems  are  the  most 
popular,  and  as  positive  driven  pumps  are  resorted  to,  to  feed  the 
oil,  the  general  tendency  is  to  provide  oil  leads  of  a  large  diam- 
eter and  to  reduce  the  number  of  bends  to  a  minimum.  Whenever 
bends  are  necessary  they  should  be  made  as  large  as  possible  to 
reduce  the  obstructions  and  resistance. 

From  the  above  it  can  readily  be  understood  that  the  writer 
considers  the  constant  level  splash  recirculating  system  the  sim- 
plest in  use  at  present.  Its  operation  is  mechanical  and  the  at- 
tention required  is  reduced  to  a  minimum,  while  at  the  same  time 
it  is  quite  economical  on  oil. 

The  advantages  of  the  force  feed  system  are  that  the  oil  may 
be  forced  to  the  bearings  under  separate  pressure,  reducing  the 
danger  of  the  oil  being  forced  out  by  the  bearing  pressure.  It  is 
generally  agreed  that  with  force-feed  the  specific  pressure  on  the 
bearing  can  be  increased  and  that  the  bearing  will  last  longer, 
while  on  the  other  hand  the  writer  finds  that  this  system  is  more 
expensive  to  install  and  less  economical  of  oil.  It  would  appear 
to  be  better  adapted  to  commercial  car  engines  which  operate  at 
or  near  their  full  load  for  a  considerable  length  of  time. 

In  the  gravity  feed  system  the  oil  leads  must  be  carried  on  the 
outside  of  the  motor,  which  presents  some  complications,  as  they 
will  require  attention  at  intervals.  The  economy  is  possibly  on  a 
par  with  the  constant  level  splash  system.  Mechanical  oilers  are 
very  rarely  used  on  the  types  of  commercial  cars,  being  prac- 
tically obsolete. 


CHAPTEK  III 

THE  MOTOR  COOLING  SYSTEM 

CONTINUING  from  the  previous  chapter  we  can  next  investi- 
gate the  cooling  system,  considering  first  the  office  of  the  cooling 
system.  This  system  must  cool  the  cylinder  walls  to  such  an  ex- 
tent as  to  permit  of  the  proper  lubrication  and  to  prevent  the 
carbonization  of  the  lubricating  oil.  Preignition  will  also  occur 
if  the  metal  is  permitted  to  heat  to  a  red  heat,  causing  the  gas  to 
ignite  on  the  compression  stroke.  It  is  the  general  impression 
that  the  office  of  the  cooling  system  is  to  abstract  the  heat  from 
the  gases  within  the  cylinders,  this  heat  having  been  generated  by 
the  explosion.  This  is  not  the  case,  for,  as  a  matter  of  fact,  the 
duty  of  the  cooling  medium  is  to  keep  the  cylinder  walls  cool,  the 
heat  of  the  gases  being  converted  into  useful  energy. 

The  Direct  or  Air  System. — There  are  two  general  types  of 
cooling  systems,  the  direct  or  air  system  and  the  indirect  or  a 
system  using  a  cooling  medium  such  as  water  or  oil.  The  term 
direct  is  applied  to  the  air  system,  as  there  is  no  intermediate 
transfer  of  heat  from  the  cylinder  walls  to  the  radiating  surfaces 
by  means  of  a  cooling  liquid.  Air  cooling  is  generally  effected 
by  cooling  ribs  or  fins  as  they  are  sometimes  called,  cast  integral 
with  the  cylinder  walls  and  head.  Some  mechanical  method,  such 
as  mounting  a  fan  at  front  of  the  motor,  or  combining  it  with  the 
fly  wheel,  is  generally  resorted  too  for  inducing  air  circulation. 
Fig.  29  illustrates  a  typical  air  cooling  system.  This  type  of 
cooling  system  is  most  popular  on  the  low-priced  vehicles  using 
two,  three  and  four-cylinder  motors.  It  may  be  used  on  either 
two  or  four-cycle  motors. 

The  Indirect  System — Water  or  Oil. — The  indirect  cooling 
system  as  mentioned  above  involves  the  circulation  of  a  liquid 
such  as  water  or  oil,  to  absorb  the  heat  and  deliver  same  to  a 
current  of  air  which  is  passed  over  the  surface  of  the  radiator 
within  which  the  liquid  in  its  heated  state  is  circulated.  At 
present  water  is  used  as  the  medium  in  all  indirect  systems.  Oil 
was  used  in  some  cases,  but  it  presented  serious  disadvantages. 
Water  may  be  circulated  in  two  ways,  first  by  the  natural  system 

39 


40      MOTOR  TEUCK  DESIGN  AND  CONSTRUCTION 

which  is  termed  the  thermo-syphon  system,  and  second  under 
pressure  through  the  use  of  a  suitable  pump  driven  by  the  engine. 


FIG.  29.     Sectional  View  of  an  Air-Cooled  Motor. 

The  indirect  system  may  be  described  as  follows :  Water  is  cir- 
culated from  the  lower  water  tank  of  the  radiator  through  a  dis- 
tributing manifold  to  the  lowest  point  of  the  cylinder  water 
jackets,  and,  as  it  becomes  heated,  its  specific  gravity  decreases, 
rises  and  flows  out  through  the  outlet  manifold  located  on  the 
top  of  the  cylinders,  to  the  top  of  the  radiator,  passing  into  the 
upper  tank.  From  here  it  is  distributed  to  various  water  pas- 
sages through  which  it  passes  to  lower  tank  and  is  recirculated. 
These  water  passages  are  separated  by  air  spaces  for  heat 
radiation. 

In  the  forced  circulation,  a  pump  draws  water  from  the  lower 
tank  and  forces  it  through  cylinders,  as  well  as  creating  a  pres- 


THE  MOTOR  COOLING  SYSTEM 


41 


sure  to  force  it  through  the  water  passages  of  the  radiator.  In 
the  thermo-syphon  system,  the  pump  is  eliminated  and  circula- 
tion is  induced  by  the  heat  of  the  motor.  The  water  under  the  in- 
fluence of  heat  sets  up  a  circulation.  It  can  readily  be  understood 
that  the  heat  replaces  the  pump  and 
acts  as  the  moving  force  on  the  water.  WATER 

Types  of  Radiators. — Many  different  INLET 
types  of  radiators  have  been  worked  out 
since  the  early  days  of  the  industry. 
The  types  in  use  at  present  are  termed 
the  honeycomb,  cellular,  vertical  tube 
and  vertical  tube  built-up  types.  The 
radiator  is  necessarily  comprised  of  an 
upper  and  lower  water  tank  and  the 
core  in  which  the  water  is  divided  into 
small  streams,  which  are  separated  by 
air  passages  for  heat  radiation  as  shown 
in  Fig.  30.  The  type  of  radiator  is  gen- 
erally defined  by  the  type  of  core  used. 

The  true  honeycomb  core  consists 
of  a  series  of  six-sided  or  hexagonal- 
shaped  tubes  fastened  into  the  water 
tanks  in  such  a  way  as  to  allow  of  air  space  between  the  water 
passages.  This  type  is  frail  and  not  to  the  writer's  knowl- 
edge in  use  at  present  on  commercial  cars. 

The  more  popular  cel- 
lular core  is  often  called  a 
honeycomb.  This  consists 
of  a  series  of  square  tubes 
placed  either  vertically  or 
diagonally  into  the  tank, 
forming  a  much  more  rigid 
structure.  The  vertical 
placing  is  more  desirable, 
as  this  provides  a  contin- 


uous vertical  tube  from  one 
tank  to  the  other.    It  offers 
FIG.  31.    Section  of  Cellular  Type  Core,   less  resistance  to  circulation 

and  is  not  so  apt  to  clog  up 

from  dirt,  rust  and  other  substances.  Radiating  surfaces  are  ap- 
proximately equal  for  either  construction.  This  construction  is 
clearly  illustrated  in  Fig.  31. 


OUTLET* 

LOWER 

FIG.  30.     Cutaway 
Section  of  Radiator. 


CELLULAR 
TYPE  CO&E 


WATER 


A/P'^£te 
SPACES  -^ 


AIP 


42      MOTOE  TRUCK  DESIGN  AND  CONSTRUCTION 


FIG.  32. 


The  vertical  tiibe  type  of  core  consists  of  a  series  of  rectangu- 
lar tubes  fastened  into  the  water  tanks,  with  fins  attached  to 
them  for  heat  radiation,  as  shown  in  Fig.  32.  The  fins  also  ma- 
terially assist  in  strengthen- 
ing the  core,  and  in  some 
cases  they  are  made  contin- 
uous so  that  the  entire  con- 
struction presents  a  very 
pleasing  appearance,  similar 
to  the  cellular  type.  This  ver- 
tical tube  type  of  radiator  is 
very  much  in  evidence  on  the 
popular-priced  vehicles,  as  its 
first  cost  is  considerably 
lower  than  the  cellular  type. 
During  the  past  few 
years  there  has  been  a  decided 
tendency  to  build  up  radiator 
cores  from  round  copper 
tubes  with  separate  round  or 
square  cooling  fins  and  cast 
p  water  tanks,  the  upper  tank 

usually  being  provided  with  ribs  to  assist  in  heat  radiation  owing 
to  thicker  section  of  metal  neces- 
sary in  casting  these  tanks.  This 
type  of  radiator  is  illustrated  in 
Fig.  33  with  a  tubular  core  and 
cast  columns  between  the  tanks  to 
relieve  the  core  of  the  strains  due 
to  the  weight  of  the  tanks  and 
water. 

Another  popular-priced  truck 
uses  this  style  of  radiator.  How- 
ever, the  tubes  are  fastened  to  the 
tanks  by  clamps  in  series  of  three. 
This  construction  presents  an  ad- 
vantage in  the  simplicity  of  re- 
pair and  the  small  cost  of  replac- 
ing these  sections  should  they  be 

damaged  beyond  repair.     While  this  type  of  radiator  presents 
some  advantages  in  strength,  the  writer  believes  that  it  pos- 


Section  of  Vertical  Tube 
Type. 


FIG.  33.     Cast  Water  Tanks  and 
Built-Up   Core. 


THE  MOTOR  COOLING  SYSTEM 


43 


sesses  a  disadvantage  in  that  it  is  not  as  efficient  as  the  conven- 
tional style  mentioned  above.  Only  a  certain  portion  of  the 
tubes  is  exposed  to  the  air  currents,  while  the  rear  ones  are 
naturally  limited  in  cooling  ability,  owing  to  being  obstructed  by 
the  forward  ones.  The  volume  of  water  is  somewhat  greater  in 
these  tubes  for  the  same  rate  of  circulation,  so  that  the  cooling 
effect  is  somewhat  retarded.  The  writer  has  experimented  with 
both  types  and  has  come  to  the  conclusion  that  the  conventional 
type  is  more  efficient  and  will  stand  up  under  the  most  severe 
service  when  spring-mounted. 


FIG.  34.     Mack  Model   "AC"  Built-up-Radiator. 

An  unusual  radiator  construction  is  shown  in  Fig.  34,  which 
represents  the  Mack  radiator  for  heavy  duty  trucks.  By  the  use 
of  a  large  number  of  practically  semi-circular  sections  of  copper 
tubes,  which  are  expanded  into  plates  that  in  turn  are  bolted  to 
the  upper  and  lower  tanks,  a  solderless  radiator  is  obtained, 
which  expands  within  itself  and  withstands  severe  vibration  with- 
out failure.  Upper  and  lower  tanks  are  of  aluminum  alloy  and 
the  upper  tank  forms  part  of  the  cowl,  while  the  lower  is  part  of 
the  frame  that  supports  the  entire  unit.  The  tubes  are  expanded 
into  the  plates  and  no  solder  is  used  in  the  construction.  As  each 
tube  is  a  unit  in  itself,  one  or  more  of  the  tubes  can  be  blocked, 
or  pinched  off  in  case  of  emergency  without  interfering  with 
others.  Instead  of  being  placed  in  front  of  the  engine  this  ra- 
diator is  placed  back  of  it. 


44   MOTOE  TRUCK  DESIGN  AND  CONSTRUCTION 


Mounting  of  Radiators. — Radiators  may  be  mounted  in  two 
positions  on  the  chassis  frame;  either  in  front  of  the  car  so  that 
the  air  currents  pass  almost  unobstructed  through  the  passage- 
ways, or  in  back  of  the  engine  against  the  dashboard,  while  on 
one  particular  chassis  it  is  placed  in  the  rear  of  the  engine  under 
the  seat.  Either  of  the  latter  two  positions  afford  a  somewhat 
more  accessible  engine  and  also  afford  a  better  protection  for  the 
radiator.  However,  this  construction  requires  a  proportionately 
larger  radiator  to  obtain  the  same  results  as  in  the  forward 
position. 

In  commercial  car  operation  the  heavy  vibrations  accompany- 
ing high  speed  on  rough  pavements  and  the  distortion  of  the 

frame,  place  heavy  strains 
on  the  radiator,  so  that  it 
becomes  necessary  to  mount 
it  on  springs  and  also  pro- 
vide a  certain  amount  of 
universal  movement  to 
overcome  frame  distortion. 
These  springs  maj'  be  of 

FIG.  35.     Combined     Enclosed     Spring    flat    spiral    or    coiled    wire 
with  Front  Hanger  Brackets.  or  of  round  Or  square  sec- 

tion.  This  support  is  usu- 
ally of  a  three-point  type,  so  that  a  limited  amount  of  universal 
movement  is  obtained. 

Fig.  35  shows  a  popular 
type  of  enclosed  spring 
mounting  combined  with  the 
front  spring  hanger  brackets. 
Brackets,  riveted  to  each  side 
of  the  radiator,  have  exten- 
sions, which  are  mounted  be- 
tween two  coiled  wire  springs 
in  each  spring  bracket.  This 
bracket  has  a  small  cover  plate 
which  retains  the  springs,  FIG.  36. 
and,  together  with  the  spring 
bracket,  supports  a  vertical 

shaft,  which  acts  as  a  guide  for  the  radiator  brackets.  The 
radiator  brackets  are  drilled  out  larger  than  the  shaft,  to  pro- 
vide for  a  certain  amount  of  universal  movement.  The  top  of 


Universal  Enclosed  Spring 
Mounting. 


THE  MOTOK  COOLING  SYSTEM 


45 


the  radiator  is  further  supported  by  a  stay  rod  which  is  attached 
to  the  dashboard.  A  bumper  extending  from  one  spring  bracket 
to  the  other  protects  the  radiator  core  from  being  damaged  by 
colliding  with  the  rear  end  of  other  vehicles. 


FIG.  37.     Flat  Spiral  Spring-  Mounting  of  the  Master  Trucks. 

Fig.  36  illustrates  another  type  of  spring  mounted  radiator. 
However,  in  this  case  a  limited  universal  movement  is  obtained 
through  a  clevis  joint  on  the  frame  bracket,  while  the  bumper  is 
set  into  the  main  frame  channel. 


FIG.  38.     Onieda  Eadiator  Mounting. 


46      MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


Various  constructions  are  resorted  to  in  practice.  However, 
they  merely  present  different  methods  of  accomplishing  the  same 
results. 

Fig.  37  shows  a  construction  using  a  flat  spiral  spring  attached 
to  the  radiator.  One  end  of  the  flat  spiral  spring  is  bolted  to  the 
upper  flange  of  the  frame  member,  while  the  other  end  is  rolled 
into  an  eye.  A  bolt  is  inserted  through  the  spring  and  side  col- 
umn to  form  a  permanent  fastening. 

An  excellent  example  of  flexible  mounting  is  depicted  in  Fig. 
38  in  which  a  pneumatic  shock  absorber  is  used.  This  shock  ab- 
sorber consists  of  a  pneumatic  rubber  sphere  placed  within  a 
chamber  of  elliptic  shape,  providing  a  perfect  cushion  and  acts 
as  a  pivot,  while  it  is  perfectly  enclosed  and  protected  from  dirt 
and  grit.  This  sphere  is  protected  against  excessive  wear  by 
fabric  pads  set  into  the  cups  which  form  the  chamber.  These  are 
free  to  roll  in  any  direction  on  the  sphere,  thereby  relieving  all 
warping  stresses,  while  the  spheres  take  up  all  shocks  and 
vibrations. 

Types  of  Water  Pumps. — There  are  four  general  types  of  water 
pumps:  the  gear,  the  centrifugal,  the  rotary  or  vane  and  the 
plunger  types.  The  centrifugal  is  by  far  the  most  popular  and 


Wafer  Outlet 


Water  Inlet 


Pump 
Casing 


Packing 
sG!cmd 


ump  Shaft 


Drain  Plug 


Connection 
Jo  Radiator 


FIG.  39.     Sectional  View  of   Centrifugal  Pump. 


THE  MOTOR  COOLING  SYSTEM 


47 


INLET 


the  gear  type  is  next  in  popularity,  while  the  rotary  or  vane  type 
is  very  little  used  on  commercial  car  motors.  The  plunger  type 
is  entirely  confined  to  marine  work,  where  it  is  used  to  better 
advantage. 

The  centrifugal  type  illustrated  in  Fig.  39  is  perhaps  the  sim- 
plest of  all  and  the  easiest  to  understand.  It  consists  of  an  im- 
peller of  paddlewheel  which  may  either  be  formed  integral  with 
or  keved  to  the  driving  shaft  and  a  case  and  cover  which  house 
the  rotating  member.  In 
operation  it  is  rotated  at  a 
high  speed,  the  water  en- 
tering at  the  center  of  the 
rotating  member,  flowing 
out  on  the  arms  or  paddles 
and  being  thrown  off  by 
centrifugal  force.  This 
throwing  off  action  is  re- 
stricted by  the  case,  so  that 
the  water  is  forced  through 
the  pump  outlet. 

The  gear  type  of  water 
pump  is  identical  with  the 

gear  type  of  oil  pump,  with  the  exception  of  being  much  larger. 
It  is  illustrated  in  Fig.  40  and  it  can  readily  be  seen  that  it  con- 
sists of  a  pair  of  gears,  a  pair  of  shafts  for  them  to  rotate  on  and 
a  case  with  cover  to  serve  as  a  housing  for  the  gears  and  to  carry 
the  shaft  bearings.  The  arrows  illustrate  how  the  water  enters 
the  housing  through  the  inlet  pipe  and  is  carried  around  between 
the  spaces  of  the  gear  teeth  and  forced  out  through  the  pump 
outlet  on  the  opposite  side  of  the  inlet.  This  type  of  pump  is 
quite  simple  and  was  extensively  used  on  the  earlier  types  of 
commercial  cars. 

Both  the  gear  and  centrifugal  types  of  pumps  possess  an  ad- 
vantage over  other  types,  in  that  they  provide  a  continuous 
stream  of  water.  Between  the  two  there  is  very  little  or  no  choice, 
unless  it  is  that  the  gear  pump  is  more  likely  to  become  noisy. 
They  both  do  the  work  under  substantially  the  same  conditions. 

The  rotary  or  sliding  vane  pump  shown  in  Fig.  41  consists  of 
a  cylindrical  housing  in  which  is  located  a  disc  of  a  thickness 
equal  to  the  internal  height  of  the  housing,  but  of  smaller  diam- 
eter. The  disc  is  located  eccentrically  with  respect  to  the  cham- 


FIG.  40.    Section  of  Gear  Pump. 


48   MOTOE  TRUCK  DESIGN  AND  CONSTRUCTION 


SLID/NO  VANES 


her  and  is  cut  with  a  diametrical  slot  dividing  it  into  two  halves, 
in  which  slots  are  located  two  sliding  vanes  which  are  pressed 
apart  by  a  flat  spring  between  them,  the  action  of  the  vanes 

being  to  carry  the  water 
around  to  the  outlet  as  in- 
dicated by  the  arrows. 

Water  pumps  are  gen- 
erally driven  by  shafts 
extending  from  timing 
gear  housing  and  are  pro- 
vided with  flexible  or  uni- 
versal driving  couplings. 
The  couplings  serve  to 
keep  the  pump  free  from 
strains  due  to  misalign- 
FIG.  41.  Section  of  Sliding  Vane  Pump,  ment,  and  they  are  gener- 
ally so  designed  that  when 

the  pump  freezes  up,  the  coupling  will  break  before  any  damage 
is  done  to  the  pump  parts. 

Fans  as  an  Auxiliary. — The  motor  must  be  cooled  effectively 
regardless  of  car  speed.  To  cool  a  commercial  car  motor  under 
ideal  conditions  and  most  effectively  would  require  a  tremen- 
dously large  radiator,  if  the  car  stood  still  and  only  natural  air 
circulation  were  depended  upon.  To  reduce  the  radiator  to  a 
size  that  can  be  used,  the  relative  efficiency  is  increased  through 
an  artificial  flow  of  air.  This  is  brought  about  in  two  ways.  One 
is  that  the  radiator  does  not  stand  still,  but  is  moved  with  the  car, 
which  induces  an  air  circulation.  However,  this  would  not  be 
effective  with  the  car  standing  still  and  the  engine  running,  so  a 
second  artificial  circulation  is  provided  through  a  fan.  This  fan 
is  driven  from  the  engine  and  rotates  when  the  engine  rotates. 
If  the  engine  runs  slowly  and  has  little  heat  to  dispose,  the  fan 
runs  slowly.  Again,  when  the  engine  is  running  at  its  maximum 
speed,  the  fan,  too,  is  making  its  highest  possible  number  of  revo- 
lutions." The  fan  serves  the  same  purpose  in  an  air-cooling  sys- 
tem, by  forcing  a  draught  of  air  over  the  cylinders  in  each 
revolution. 

This  fan  is  generally  placed  at  the  front  of  the  motor  and 
driven  by  belt  from  a  pulley  mounted  on  the  crank  shaft,  cam 
shaft,  or  accessory  drive  shaft,  and  draws  air  through  the  radi- 
ator, while  in  the  air-cooled  system  it  draws  air  through  a  screened 
opening  at  the  front  of  the  hood. 


THE  MOTOK  COOLING  SYSTEM  49 

Sometime  ago  there  was  a  decided  tendency  to  combine  the 
fan  with  the  flywheel,  drawing  air  through  the  radiator  and  over 
the  whole  engine,  thus  effecting  a  secondary  method  of  cooling. 
In  some  air-cooling  systems  the  bonnets  on  the  engine  are  pro- 
vided with  deflectors  so  as  to  direct  the  air  currents  to  the  rear 
cylinders,  while  one  maker  encloses  the  entire  motor  in  a  sheet 
steel  housing,  so  the  flywheel  draws  an  equal  amount  of  air  over 
each  cylinder. 


5 


CHAPTEE  IV 

CAKBUEETION  AND  CAEBURETOES 

CARBURETION  is  the  term  applied  to  the  process  of  converting 
the  liquid  fuel  into  an  explosive  mixture.  It  comprises  the 
vaporization  of  the  fuel  and  the  mixing  of  gasoline  and  air  in 
the  proper  proportion  to  produce  the  explosive  mixture  drawn 
into  the  cylinders.  The  function  of  the  air  is  to  supply  oxygen 
for  combustion. 

Air  is  a  quantity  of  infinite  variables,  since  its  oxygen  con- 
tent for  a  given  volume  is  proportionate  to  its  temperature.  The 
higher  the  temperature,  the  smaller  the  quantity  of  oxygen  it 
contains,  without  any  change  of  carburetor  adjustment.  It  is  ac- 
cordingly advisable  to  use  the  air  at  the  lowest  temperature  at 
which  vaporization  is  possible. 

The  best  proportion  of  air  to  gasoline  varies  between  sixteen 
to  seventeen  parts  of  air  to  one  of  gasoline ;  however,  this  will  be 
dependent  upon  the  quality  of  the  fuel. 

Since  the  power  of  a  gasoline  motor  is  derived  from  the  fuel 
which  enters  the  cylinders  during  the  suction  stroke,  it  is  df 
utmost  importance  that  the  mixture  of  fuel  and  air  which  is  used 
by  the  motor,  shall  always  be  of  exact  proportions,  so  that  when 
it  is  ignited  by  the  spark,  it  will  give  the  maximum  force  of  ex- 
plosion for  a  given  quantity  of  fuel.  If  there  is  too  much  fuel  or 
too  little,  within  relative  narrow  limits,  the  action  of  the  engine 
becomes  objectionable. 

Vaporization  of  fuel  may  be  accomplished  in  two  ways,  by 
heat  or  vacuum;  vaporization  due  to  pressure  reduction  is  dis- 
tinguished from  vaporization  caused  by  the  supplying  of  heat. 
In  the  vacuum  method,  vaporization  is  only  partly  complete,  no 
matter  how  far  the  process  of  reduction  is  carried,  since  the  part 
of  the  liquid,  which  vaporizes,  does  so  through  the  abstraction  of 
heat  from  the  remainder,  which  becomes  constantly  colder  until 
finally  the  temperature  is  so  low,  that  vaporization  ceases  until 
heat  is  supplied  from  some  outside  source.  When  vaporization 
is  brought  about  entirely  by  heat  from  an  outside  source,  the 
degree  to  which  it  may  be  carried  depends  wholly  on  the  amount 

50 


CARBURETION  AND  CARBURETORS      51 

of  heat  supplied,  since  the  temperature  of  the  liquid  is  being  con- 
stantly raised  to  or  maintained  at  the  proper  point. 

In  practice  neither  of  the  above  processes  are  carried  to  the 
limit,  but  both  act  together.  The  reduced  pressure,  due  to 
('  motor  suction,"  causes  vaporization  with  a  lowering  of  the  tem- 
perature, and  the  heat  of  the  air  tends  to  cause  vaporization 
through  a  transfer  of  heat  from  itself  to  the  liquid.  Each  of 
these  vaporizing  actions  assist  the  other;  the  air  supplying  heat 
to  the  liquid  as  it  is  cooled  by  vaporization  under  reduced  pres- 
sure, and  the  reduction  in  temperature,  due  to  pressure  reduc- 
tion, facilitating  the  transfer  of  heat  from  the  air  to  the  liquid. 

The  instrument  which  serves  to  carry  out  the  above  functions 
is  known  as  the  carburetor.  Gasoline  is  stored  in  a  tank,  gen- 
erally located  under  the  driver's  seat,  and  from  here  it  is  fed 
through  a  small  pipe  to  a  compartment  of  the  carburetor  called 
the  float  chamber,  passing  through  a  needle  valve  and  strainer, 
which  regulates  the  amount  of  gasoline  entering  the  carburetor. 
To  allow  metal  floats  to  be  sustained  in  the  gasoline  they  are 
made  air  tight  and  hollow,  so  that  the  needle  valve  can  pass 
through  them  onto  the  valve  seating.  Somewhere  near  the  top 
of  the  needle  valve,  small  weighted  arms  are  pivoted,  the  ends  of 
which  rest  idly  on  the  top  of  the  float.  The  function  of  this  float 
and  chamber  is  to  maintain  a  constant  level  of  gasoline  in  its  own 
chamber  and  the  chamber  in  which  the  jet  is  located.  The  level 
in  the  latter  chamber  must  be  constant  so  as  to  prevent  the  gaso- 
line flooding  over  the  jet,  which  will  cause  faulty  running  of  the 
engine.  The  action  of  the  float  is  very  much  like  an  automatic 
water  cistern,  with  its  ball  valve,  for,  as  more  gasoline  enters  the 
first  chamber,  the  float  rises,  and  with  it  the  weights  resting  on  it 
eo  that  the  needle  valve  is  pushed  down  on  its  seating  and  shuts 
off  the  supply. 

The  other  part  of  the  carburetor  called  the  choke  tube,  or 
mixing  chamber,  accommodates  the  jet  and  allows  a  stream  of 
air  to  pass  around  it  when  the  piston  descends  on  the  suction 
stroke.  The  float  chamber  maintains  a  constant  level  of  gasoline 
in  the  jet.  When  the  air  rushes  up  around  the  jet,  it  draws  with 
it  a  certain  amount  of  sprayed  gasoline,  and,  when  the  mixture 
of  air  and  gasoline  impinges  on  the  sides  of  the  inlet  manifold,  it 
becomes  a  gaseous  mixture  and  enters  the  engine  in  this  state 
through  the  inlet  valve. 

Just  below  the  manifold  flange  of  the  carburetor,  and  in  the 
choke  tube,  is  located  a  throttle,  which  can  be  opened  or  closed 


52      MOTOE  TEUCK  DESIGN  AND  CONSTEUCTION 

by  the  operator  from  the  lever  on  the  steering  gear  or  foot 
throttle.  The  more  gas  the  engine  can  receive,  the  faster  it  runs, 
and  the  faster  it  runs,  the  more  gasoline  it  is  likely  to  draw  from 
the  jet.  This  would  give  an  unduly  rich  mixture,  unless  means 
were  provided  for  admitting  more  air,  and  thus  giving  the  mix- 
ture approximately  correct  proportions.  For  this  purpose  an 
auxiliary  air  valve  is  provided,  communicating  with  the  choke 
tube  just  above  the  jet.  As  the  engine  speed  increases,  this  auxil- 
iary air  valve  opens  and  permits  more  air  to  enter,  thus  main- 
taining the  proper  mixture.  It  is  a  general  assumption  that  more 
air  must  be  admitted  at  high  speeds,  but  this  is  not  really  correct ; 
for,  while  we  are  admitting  more  air,  we  are  merely  endeavoring 
to  keep  the  proportions  of  air  and  gasoline  the  same.  Increased 
engine  speed  means  increased  suction  on  the  jet,  and  naturally 
the  liquid  gasoline  is  drawn  through  faster  than  the  air,  so  that 
more  air  must  be  admitted  to  compensate  for  the  excessive  suc- 
tion. But  apart  from  speed,  temperature  and  humidity  have 
their  effect  on  carburetion.  In  the  summer,  the  air  parts  require 
to  be  opened  wider  than  in  winter,  as  the  atmosphere  is  less 
dense;  also,  when  the  air  is  damp  and  the  barometer  low,  more 
air  will  be  necessary. 

The  auxiliary  air  valves  are  generally  suction  operated,  open- 
ing progressively  as  the  suction  increases  from  higher  speed  or 
some  other  cause.  If  these  valves  could  be  made  to  have  no  in- 
ertia, they  would  follow  the  suction  exactly  and  their  action 
would  be  ideal.  But  the  fact  is  that  they  open  and  close  late. 
Added  to  these  faults,  is  that  there  is  no  way  of  operating  them 
that  is  not  subject  to  variation.  If  springs  are  used  they  will 
change  in  strength.  A  weight  is  effected  by  vibrations  of  the 
car,  as  is  also  a  mercury  bath  with  a  float,  though  to  a  less  extent. 
In  fact  numerous  methods  have  been  experimented  with  and  all 
found  lacking  in  some  respect. 

There  are  many  different  makes  of  carburetors  in  use  on  com- 
mercial car  engines  at  present.  All  carburetors  which  are  used 
at  the  present  time  work  by  controlling  the  flow  of  gasoline  in 
proportion  to  the  air  demand,  some  attempting  this  by  raising  the 
gasoline  needle  valve  with  the  increased  demands  of  the  motor, 
such  as  the  Schebler  and  Breeze  carburetors;  and  others  accom- 
plishing this  indirectly  through  various  air  regulations  and  auxil- 
iary valves,  as  in  the  Kingston,  Stromberg  and  others. 

Some  carburetors  operate  automatically,  while  others  are  so 
arranged  that  they  may  operate  both  automatically  and  me- 
chanically. 


CARBUKETION  AND  CAKBUEETOKS 


53 


This  principle  of  automatic  carburetion,  which  is  employed 
in  the  majority  of  modern  carburetors,  may  be  outlined  as 
follows : 

A  correct  mixture  having  been  obtained  for  the  minimum 
suction  on  which  the  motor  is  capable  of  running,  is  compensated 
by  the  introduction  of  additional  air  at  a  rate  varying  auto- 
matically with  the  suction.  The  mechanical  operation  is  obtained 
by  connecting  the  butterfly  valve,  which  controls  the  admission 
of  gases  from  the  carburetor,  writh  the  butterfly  valve  in  the 
main  air  opening,  the  automatic  operation  of  the  auxiliary  valve 
being  retained. 

During  the  past  year  there  has  been  a  tendency  to  provide 
dashboard  adjustments,  so  that  the  mixture  may  be  instantly 
varied  throughout  the  entire  range  for  heavier  or  lighter  work, 
or  because  of  other  changing  conditions.  This  is  generally  ac- 
complished by  varying  the  pressure  of  the  auxiliary  air  valve 
spring.  They  are  quite  an  advantage,  as  it  is  claimed  that  an 
automatic  carburetor  cannot  adapt  itself  to  changes  in  gasoline 
density,  or  in  humidity,  or  to  the  gradual  warming  up  of  an 
engine  when  started  from  cold. 

It  would  require  too  much  space  to  illustrate  all  the  various 
makes  of  carburetors  used  on  the  various  commercial  car  engines, 
so  the  writer  will  present  a 
few  illustrations,  which  are 
explanatory  of  the  various 
types  discussed  in  this  ar- 
ticle, such  as  the  raised 
needle  valve  type,  the  indi- 
rect type,  and  automatic 
and  mechanically  operated 
types. 

Fig.    42    is    a    sectional 
view    of    the    Model    "L" 
Schebler  carburetor,  which 
is  of  the  raised  needle  type, 
and  is  so  designed  that  the 
amount  of  fuel  entering  the 
motor  is  automatically  con- 
trolled by  means  of  a  raised  needle  seating  in  the  jet,  working 
automatically  with  the  throttle.     The  float  and  its  chamber  sur- 
round the  main  air  supply  in  which  the  jet  is  located.     The  jet 


THROTTLE   lfV£a 


FLOAT  CHAMBER 


FIG.  42.     Sectional  View   of   Schebler 
Carburetor. 


54   MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


FLOAT 


FIG.  43. 


Section   of   Kingston   Car- 
buretor. 


opening  is  controlled  by  a  needle,  which  permits  of  a  variable 
opening  as  the  throttle  is  opened  or  closed,  being  operated  by  a 

cam  on  the  throttle  lever. 
The  auxiiiary  air  valve  is 
controlled  by  the  suction  of 
the  motor,  while  the  mix- 
ing chamber  is  water  jack- 
eted to  apply  heat  to  assist 
in  vaporization.  The  main 
air  supply  can  also  be  con- 
nected with  a  drum  around 
the  exhaust  manifold  for 
supplying  warm  air. 

Fig.  43  is  an  illustra- 
tion of  the  Kingston  car- 
buretor, which  is  provided 
with  an  adjustable  jet  sur- 
rounded by  the  float  and 
chamber.  The  main  air  in- 
•  take  communicates  with 

the  mixing  chamber,  while  the  auxiliary  air  enters  through  five 
circular  openings  ar- 
ranged in  a  semi-circle 
above  the  mixing  cham- 
ber, and  controlled  by 
floating  balls.  These  balls 
are  so  arranged  that  they 
cannot  become  displaced. 
They  operate  automat- 
ically, gradually  lifting 
from  their  seats  as  the 
motor  suction  increases. 
The  air  passing  the  open- 
ings guarded  by  the  balls 
has  an  unrestricted  pas- 
sage into  the  mixing 
chamber,  and  then  to  the 
motor.  The  main  air  in- 
take is  fitted  with  a  but- 
terfly throttle,  so  that  the 
amount  of  air  can  be  reduced  for  starting,  around  the  nozzle  of 


JET  ADJUSTING 
SCREEN 


FIG.  44.     Holley  Carburetor  in  Section. 


CARBURETION  AND  CARBURETORS 


55 


THROTfLC  VALVE 


the  jet,  is  a  well,  which  becomes  partially  filled  with  gasoline 
while  the  motor  is  idle.  This  is  brought  about  automatically  by 
the  level  of  the  gasoline  in  the  float  chamber  being  slightly  higher 
than  the  top  of  the  jet.  This  gives  a  rich  mixture  for  starting, 
and  as  long  as  the  motor  is  running  the  gasoline  is  drawn  through 
the  jet  into  the  intake  manifold,  the  well  remaining  dry. 

Some  of  the  features  of  the  Holley  carburetor,  illustrated  in 
Fig.  44,  are  concentric  float,  adjustable  jet,  supplementary  stand- 
pipe  for  starting  and  slow  running  and  absence  of  air  valves. 
Gasoline  enters  and  passes  through  a  strainer  A  and  passages  H 
into  the  jet.  This  jet  is  controlled  by  a  milled  screw,  so  that  the 
opening  can  be  varied  at  will.  Gasoline  passes  into  the  jet  M, 
which  is  in  the  shape  of  a  venturi,  or  double-ended  cone,  and  also 
into  the  standpipe  /,  to 
a  level  determined  by  the 
float.  This  standpipe 
leads  to  the  edge  of  the 
butterfly  throttle,  and 
when  the  latter  is  closed, 
the  suction  of  the  motor 
allows  gasoline  to  be 
drawn  up  into  the  stand- 
pipe,  past  the  plug  K,  and 
into  the  manifold.  After 
the  motor  has  been  started, 
and  the  throttle  opened, 
the  gasoline  is  drawn 
through  the  main  jet  J/, 
mixing  with  the  air  that 
enters  from  below,  through 
the  conduit  N. 

Fig.  45  illustrates  the 
Fierce-Arrow      automatic 

carburetor,  with  concentric  float  and  adjustable  jet.  The  gasoline 
supply  from  the  tank  passes  through  a  fine  gauze  strainer,  pre- 
venting water  and  dirt  from  entering  the  float  chamber.  The 
main  air  supply  is  taken  through  the  lower  inlet,  and,  coming 
from  the  proximity  of  the  exhaust  pipe,  is  warm,  and  passes  up 
around  the  spray  nozzle  A.  The  auxiliary  air  is  taken  through 
two  reed  valves,  which  are  controlled  by  flat  springs.  When  the 
engine  runs  slowly,  both  auxiliary  valves  remain  on  their  seat, 
and  as  the  engine  runs  faster,  the  more  intense  suction  opens  the 


FIG.  45.     Section   of  Fierce-Arrow   Car- 
buretor. 


56   MOTOE  TRUCK  DESIGN  AND  CONSTRUCTION 


FIG.  46. 


Sectional   View   of   Stromberg 
Carburetor. 


lighter  reed  valve,  admitting  air  above  the  spray  nozzle.  A 
further  increase  in  engine  speed  opens  the  heavier  reed  valve,  per- 
mitting still  more  air  to 
enter. 

The  Stromberg  carbu- 
retor (Fig.  46)  is  a  double 
jet  type,  featuring  an  ec- 
centric float  chamber  with 
a  glass  wall,  a  feature 
which  is  typical  of  all 
Stromberg  models.  The 
flow  of  gases  is  controlled 
by  a  butterfly  valve  placed 
over  the  mixing  chamber 
and  immediately  over  the 
venturi,  in  which  the  main 
jet  C  is  located.  The  sec- 
ond jet,  /,  comes  into  op- 
eration as  the  speed  of 

the  motor  increases  enough  to  permit  the  auxiliary  air  valve  to 
open.  The  main  air  passage  can  be  entirely  or  partially  closed 
for  starting  purposes,  and 
this  operation  also  pre- 
vents the  auxiliary  air 
valve  from  opening,  the 
latter  being  of  the  mush- 
room type,  provided  with 
two  adjustments.  The 
valve  has  two  spindles, 
one  above  and  one  below 
the  seat,  each  spindle  hav- 
ing a  spring  encircling  it, 
finer  adjustment  being 
claimed  for  this  construc- 
tion. The  body  of  the  car- 
buretor is  not  water  jack- 
eted, heat  being  supplied 
through  the  open  air  pipe 

from  a  drum  surrounding         FlG.  47.     Carter   Carburetor  in   Section. 

the  exhaust  manifold. 

The  features  of  the  Carter  carburetor,  illustrated  in  Fig.  47, 
are  eccentric  float,  shock-absorbing  needle  valve  control  and  ver- 


CARBURETION  AND  CARBURETORS      57 

tical  multiple  jet  fuel  tube.  Gasoline  enters  the  float  chamber  in 
the  usual  way.  However,  the  needle  valve  is  provided  with  a 
small  shock-absorber,  as  no  permanent  connection  is  made  be- 
tween the  float  and  the  lever  controlling  this  valve. 

The  tube,  located  in  the  funnel,  has  a  multiplicity  of  small 
holes  arranged  spirally  around  the  tube,  and,  as  a  vacuum  is 
created  in  the  carburetor  by  the  suction  of  the  motor,  the  fuel 
rises  and  falls  instantaneously  in  the  tube,  according  to  the  speed 
of  the  motor.  As  the  fuel  rises  in  the  tube,  it  is  sprayed  out  of 
the  jets,  and,  owing  to  the  minuteness  of  the  jets  and  the  force 
with  which  the  fuel  emerges,  the  gasoline  is  broken  up  into  very 
small  particles  and  converted  into  a  mist.  The  spiral  arrange- 
ment of  the  jets  insures  each  one  a  separate  supply  of  air.  This 
fuel  tube  is  adjustable  for  low  speeds,  while  the  intermediate  ad- 
justment is  obtained  through  the  auxiliary  air  valve.  The  high 
speed  adjustment  is  an  air  control  in  the  funnel  carrying  the  fuel 
tube.  A  strangling  tube  connected  with  the  float  chamber  is  also 
provided  for  easy  starting. 

Many  of  the  so-called  carburetor  troubles  are  not  really  the 
fault  of  the  carburetor  at  all.  Air  leaks  along  the  path  of  the 
gas  in  the  cylinder  will  upset  the  action  of  the  best  carburetors 
made.  The  air  leaks  may  be  caused  by  defective  gaskets  between 
the  manifold  and  the  cylinder,  or  manifold  and  carburetor,  or  by 
loose  studs,  nuts  or  cap  screws  in  these  connections.  These  air 
leaks  destroy  the  quality  of  the  mixture,  and  also  reduce  the 
vacuum  created  by  the  motor,  so  that  a  much  smaller  charge 
enters  the  cylinders.  Mixture  proportion  may  also  change,  due 
to  some  disarrangement  of  the  auxiliary  air  valve,  as  by  the 
slackening  of  the  nuts  controlling  the  spring.  On  the  present 
day  models  this  difficulty  is  overcome  by  locking  these  nuts  with 
split  pins.  Another  source  of  trouble  is  the  stoppage  of  the  feed 
line  from  the  tank  to  the  carburetor,  due  to  foreign  matter  in  the 
gasoline.  There  is  a  noticeable  tendency  this  year  towards  the 
use  of  strainers  to  remove  these  impurities. 

The  general  concensus  of  opinion  among  the  makers  of  car- 
buretors is  that,  for  commercial  car  motors,  the  mixture  should 
be  heated  by  some  means  before  entering  the  cylinders.  There 
are  numerous  ways  of  accomplishing  this,  by  water  jacketing  the 
carburetor  or  intake  manifold,  and  by  supplying  heat  from  the 
exhaust  manifold,  either  directly  to  the  mixture,  or  by  a  heat 
jacket  around  the  mixing  chamber  of  the  carburetor. 


58      MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

Carburetors  are  made  with  or  without  water  jackets,  while 
the  hot-water  supply  is  generally  taken  from  the  pump  through 
a  small  pipe  and  returned  to  the  cylinders.  The  flow  is  controlled 
by  shut-off  cocks,  so  that  it  may  be  shut  off  during  the  summer 
months,  when  better  results  are  obtained  without  the  aid  of  heat. 
Hot  air  from  the  exhaust  manifold  may  be  circulated  and  con- 
trolled in  a  like  manner. 

In  some  motors,  part  of  the  intake  manifold  passes  through 

the  water  jacket  of  the  cylinders,  so  that  heat  is  supplied  to  the 

charge.    The  direct  method  is  by  connecting  the  main  air  pipe  of 

the  carburetor  with  a  drum,  placed  around  the  exhaust  manifold, 

so  that  the  air  is  always  preheated. 

It  is  quite  difficult  to  state  which  of  the  above  methods  are  the 
best,  as  this  is  to  some  extent  dependent  upon  the  design  of  the 
carburetor.  One  method  might  work  well  on  a  certain  carburetor 
and  absolutely  fail  on  another  make. 

Carburetors  are  generally  bolted  to  flanges  of  the  intake  mani- 
fold; however,  the  heavy  vibrations  existing  in  commercial  car 
operation  have  led  some  makers  to  provide  separate  brackets  on 
the  crank  case  of  the  engine  to  take  the  weight  of  the  carburetor 
and  to  prevent  the  adjustments  from  becoming  disarranged  due 
to  the  vibration. 


CHAPTER  V 

IGNITION  SYSTEMS 

High-tension  Magnetos  of  Independent  and  Dual  Types. — A 
considerable  number  of  articles  have  been  written  on  ignition 
systems,  with  the  object  of  explaining  the  operation  of  the  mag- 
neto and  battery  systems.  However,  the  writer  will  attempt  to 
cover  this  subject  in  such  a  way  as  to  enable  the  laymen  to  ac- 
quaint themselves  with  the  action  of  the  magnetos  on  commercial 
car  motors  without  mastering  electrical  theories.  The  subject  is 
a  broad  one,  and  even  the  following  may  seem  unnecessarily  long, 
but  it  should  be  remembered  that  a  magneto  is  a  complicated  in- 
strument and  any  description  in  few  words  must  necessarily  be 
superficial  and  can  be  of  little  value. 

Three  Types. — For  ignition  purposes  the  magneto  is  at  present 
considered  the  most  efficient  device.  There  are  three  main  types 
of  magnetos  on  the  market.  First,  the  low-tension  magneto, 
with  step-up  coil,  furnishing  a  jump  spark.  Second,  the  low- 
tension  magneto  in  connection  with  the  make  and  break  system. 
Third,  the  high-tension  magneto,  furnishing  a  jump  spark. 

Low  Tension  for  Jump  Spark. — The  first  system  is  largely 
used,  having  the  advantage  of  low  first  cost,  but  necessitates  con- 
siderable complications  and  in  reality  is  a  high-tension  system; 
as  the  spark  is  made  to  jump  across  the  air  gap  between  the  spark 
plug  electrodes,  with  the  use  of  the  step-up  coil.  The  air  which 
lies  between  the  two  electrodes  is  a  non-conductor  and  is  an  ob- 
stacle to  the  flow  of  electrical  current,  so  that  a  very  high  elec- 
trical pressure  is  needed  to  send  a  spark  through  it;  therefore, 
all  different  methods  which  involve  a  spark  plug  may  be  called 
high-tension  systems.  The  ultimate  object  of  all  ignition  systems 
is  to  get  a  spark  between  two  conductors  located  in  the  engine 
cylinders. 

Low  Tension  for  Make  and  Break. — The  second  system  is  very 
rarely  used  on  commercial  cars  at  present,  being  discarded  owing 
to  its  mechanical  complications  and  the  large  amount  of  atten- 
tion required  to  keep  it  in  working  conditions.  In  this  system 
the  spark  plugs  are  discarded  and  two  conductors  are  so  arranged 

59 


60      MOTOK  TRUCK  DESIGN  AND  CONSTRUCTION 

that  they  actually  touch  each  other  in  the  cylinder.  One  con- 
ductor is  fixed  and  insulated  from  the  cylinder,  while  the  other  is 
arranged  to  be  moved  by  a  mechanical  mechanism,  so  that  a  gap 
is  created,  through  which  the  spark  passes. 

High  Tension  for  Jump  Spark. — The  third  system  is  now  the 
most  popular,  as  the  high  tension  is  produced  directly  in  the 
armature  winding  of  the  magneto,  without  the  use  of  a  coil  or 
other  auxiliary.  The  wiring  is  also  the  simplest,  as  it  consists  of 
high-tension  wires  to  each  spark  plug  and  a  low-tension  wire  to 
the  switch  on  the  dash. 

The  principal  difference  between  the  high-tension  and  the 
low-tension  ignition  systems  is,  that  in  the  high-tension  system 
there  is  an  incomplete  circuit  and  a  spark  must  be  driven  across 
an  air  gap ;  whereas,  in  the  low-tension  system  an  electric  current 
already  flowing  in  a  conducting  circuit  is  driven  by  its  own 
momentum  across  an  air  gap  which  is  suddenly  formed  on  it. 

For  high-tension,  what  is  needed  is  a  very  hot  spark  of  high 
frequency,  positive  and  of  a  certain  length  to  penetrate  the  air 
space  between  the  electrodes  of  the  spark  plugs,  which  is  gen- 
erally from  1/64  to  1/32  in. 

Basis  of  Classification. — Magnetos  are  classified  in  two  groups, 
according  to  the  basic  principles  employed  in  the  magnetic  field 
to  generate  the  initial  electrical  impulses.  These  two  classes  are 
known  as  the  armature  and  conductor  type. 

In  the  former,  electrical  current  is  generated  by  revolving 
several  thousand  feet  of  fine  copper  wire,  which  is  wound  around 
a  soft  iron  core,  between  the  pole  pieces  of  the  magneto.  As  the 
winding  rotates  within  its  narrow  confines,  electrical  impulses  are 
set  up  within  the  winding. 

The  above  types  may  again  be  divided  into  two  classes.  One 
is  called  the  primary  armature  magneto  and  the  other  is  called 
the  compound  armature  type.  The  primary  type  has  but  a  single 
winding  in  the  magnetic  field  and  generates  a  low  voltage  cur- 
rent. It  requires  an  outside  transformer  coil  to  step  up  the  cur- 
rent to  the  high  potential  required  at  the  spark  plug.  The  com- 
pound armature  type  incorporates  a  second  winding,  or  sec- 
ondary winding,  also  upon  the  armature  shaft.  In  addition,  a 
condensor  must  be  incorporated  in  the  magneto. 

The  inductor  type  consists  of  revolving  a  solid  steel  shaft, 
upon  which  are  mounted  two  steel  fan-shaped  inductor  wings, 
within  a  stationary  winding  in  the  magnetic  field. 


IGNITION  SYSTEMS  61 

High  Tension  in  Detail. — The  high-tension  magneto  is  not  only 
a  current  generator,  or  a  substitute  for  the  battery,  but  combines 
all  the  elements  of  a  complete  ignition  system  except  the  spark 
plugs  and  the  switch.  It  generates  the  current,  transforms  it  to  a 
high  pressure  and  distributes  the  high-tension  current  to  the 
cylinders. 

The  structural  portion  of  the  magneto  consists  of  permanent 
magnets  of  inverted  U-shape,  sometimes  referred  to  as  horseshoe 
magnets.  Two  such  magnets  are  generally  used  on  the  smaller 
magnetos,  while  four  are  used  on  the  larger  ones.  The  free  ends 
of  these  magnets  are  termed  the  poles,  one  as  the  north  and  the 
other  as  the  south  pole.  To  these  poles  are  secured  soft  iron 
blocks,  known  as  pole  pieces  or  pole  shoes.  The  magnets  and  pole 
pieces  are  mounted  upon  a  non-metallic  base,  while  the  pole 
pieces  are  bored  out  cylindrically  to  receive  the  armature,  which 
is  of  substantially  cylindrical  form.  This  armature  consists  of  a 
soft  iron  core  of  H  section,  and  serves  to  form  a  bridge  for  the 
magnetic  flux  between  the  pole  pieces  and  also  to  carry  the  wind- 
ing in  which  the  current  is  induced.  After  the  core  has  been 
properly  insulated,  several  layers  of  heavily  insulated  wire  are 
wrapped  around  it.  To  the  end  of  this  heavy  wire  the  beginning 
of  a  very  fine  silk-insulated  wire  is  connected  and  the  wire  is 
wound  on  the  core  until  the  slot  is  almost  filled.  After  the  outer 
insulating  cloth  is  in  place,  bands  are  put  around  the  circum- 
ference of  the  armature  to  hold  the  winding  in  place  under  high 
armature  speeds.  The  end  plates  which  form  the  shafts  are  then 
attached. 

The  heavy  or  primary  winding  serves  primarily  to  generate 
the  current,  and  in  connection  with  the  fine  or  secondary  winding, 
also  serves  to  multiply  the  pressure  or  voltage  to  such  an  extent 
that  it  will  produce  a  spark  between  the  electrodes  of  the  spark 
plug  in  the  cylinder. 

Magnetic  Lines  of  Force. — It  has  been  found  by  experiment 
that  there  is  an  attractive  and  repulsive  force  between  magnets, 
and  that  this  magnetic  force  pervades  the  surrounding  space. 
The  fact  that  a  magnet  when  suspended  near  another  magnet 
will  take  a  certain  direction,  depending  upon  the  relations  of 
the  poles,  has  led  to  the  conception  of  the  magnetic  lines  of 
force,  which  emanate  from  the  north  pole  of  the  magnet  and  pass 
through  the -surrounding  atmosphere  to  the  south  pole. 

In  a  magneto  the  magnetic  lines  of  force  flow  from  the  pole 
piece  of  the  north  pole  to  the  pole  piece  of  the  south  pole  through 


62   MOTOE  TKUCK  DESIGN  AND  CONSTRUCTION 


the  armature  and  the  air  gap  between  the  armature  core  and  the 
pole  pieces.  The  space  between  the  pole  pieces  is  termed  the  mag- 
netic field. 

The  magnetic  lines  of  force  which  pass  through  the  armature 
are  variously  distributed  according  to  the  position  of  the  arma- 
ture in  rotation.  This  is  true  because  the  magnetic  lines  of  force 
pass  more  readily  through  the  sides  of  the  H  than  through  the 
wiring  laid  between  them. 

Any  movement  of  the  armature  on  its  shaft,  either  in  making 
a  complete  revolution  or  in  oscillating  backward  and  forward, 
must  operate  to  deflect  and  distort  these  lines  of  force  in  such  a 
manner  as  to  set  up  powerful  induced  currents  in  the  armature 
winding. 

Induction  of  Electrical  Impulses. — Four  positions  of  the  mag- 
neto armature  are  shown  in  Fig.  48.  At  A  the  magnetism  is  rep- 
resented as  passing  through  the  soft  iron  core,  the  heads  of  which 
are  in  close  proximity  to  the  pole  pieces  and  threading  the  arma- 


FIG.  48.     Magneto   Armature   Positions.     A,   Magnet.     B,   Pole   Piece. 

C,  Armature. 

ture  winding.  At  B  the  armature  has  passed  to  a  point  where  its 
heads  are  just  passing  out  of  proximity  of  the  pole  pieces,  and 
thus  breaking  the  magnetic  path  between  the  pole  pieces.  At  this 
point  a  sudden  generation  of  electrical  pressure  is  taking  place 
in  the  armature  winding,  this  causing  a  current  to  flow  in  it. 
When  the  armature  reaches  position  C  its  core  again  forms  a 
path  for  the  passage  of  magnetism  from  pole  piece  to  pole  piece 
and  the  current  becomes  zero  again.  At  D  the  same  condition 
exists  as  in  B,  although  in  the  opposite  direction. 

Thus,  in  each  revolution  two  electrical  impulses  in  opposite 
directions  are  induced  in  the  primary  winding  of  the  armature. 
These  impulses  last  only  for  a  small  fraction  of  the  time  of  a 
revolution  and  are  equally  spaced.  The  electromotive  force,  or 


IGNITION  SYSTEMS  63 

tension,  of  these  is  very  low  and  entirely  insufficient  to  cause  a 
spark  to  jump  between  the  spark  plug  electrodes,  separated  by 
even  the  shortest  air  gap. 

Giving  the  Impulses  Sufficient  Strength. — The  next  step  con- 
sists in  transforming  these  impulses,  or  multiplying  their  pres- 
sure several  thousand  times.  It  is  for  this  purpose  that  the  fine 
wire  winding  is  provided  on  the  armature.  When  the  armature 
is  being  rotated  between  the  pole  pieces  an  electromotive  force 
is  being  induced  in  the  secondary  or  fine  wire  winding,  the  same 
as  in  the  primary  or  course  wire  winding  and  many  times  greater, 
but  still  not  sufficiently  great  to  bridge  the  spark  plug  electrodes. 

The  primary  winding  is  ordinarily  closed  upon  itself.  This 
causes  a  current  to  flow  in  it  more  or  less  proportional  to  the 
electromotive  force.  That  is,  the  current  is  at  a  maximum  when 
the  armature  is  in  a  vertical  position.  At  that  time  there  are 
practically  no  lines  of  force  from  the  permanent  magnets  pass- 
ing through  the  central  part  of  the  core.  But  the  heavy  current 
flowing  in  the  primary  winding  makes  of  the  core  an  electro- 
magnet, setting  up  a  magnetic  field  at  right  angles  to  that  of  the 
permanent  magnets.  Now,  if  at  this  moment  the  primary  cir- 
cuit be  suddenly  opened,  the  current  in  it  will  almost  instantly 
cease  flowing  and  the  magnetism  set  up  by  this  current  will 
vanish.  These  lines  of  force  are  also  included  by  the  turns  of 
the  secondary  winding,  and  as  they  are  withdrawn  so  exceedingly 
rapidly,  and  since  there  are  such  a  large  number  of  turns  in  the 
secondary  winding,  the  result  is  that  an  enormous  electromotive 
force  is  induced  in  the  secondary  winding,  which  will  cause  the 
spark  to  bridge  a  gap  in  the  atmosphere  of  from  one  half  to 
three  fourths  inch  long. 

The  Circuit  Breaker. — A  device  known  as  the  circuit  breaker, 
or  interrupter,  is  used  to  open  and  close  the  primary  circuit.  This 
is  carried  on  the  armature  shaft  opposite  the  driving  end  of  the 
magneto. 

It  is  represented  in  Fig.  49  and  consists  of  a  stationary  con- 
tact A  and  a  movable  contact  B  on  the  arm  C.  Both  of  these 
parts  are  mounted  on  a  brass  disc  Z>,  which  is  securely  fastened 
to  the  armature  shaft  and  rotates  with  it.  The  stationary  con- 
tact A  is  insulated  from  the  disc  />,  while  the  movable  contact  B 
is  in  metallic  contact  with  it,  and  the  disc  D  is  grounded  to  the 
frame  of  the  magneto  by  a  grounding  brush.  The  circuit  breaker 
is  surrounded  by  a  cylindrical  housing  F,  to  the  interior  of  which 


64      MOTOE  TKUCK  DESIGN  AND  CONSTRUCTION 

at  diametrically  opposite  points  are  secured  steel  cam  blocks, 
G-G.  Ordinarily  these  two  contact  points  are  kept  in  contact  by 
a  spring.  As  the  disc  D  rotates,  the  outer  end  of  the  arm  C  comes 
in  contact  with  the  cam  blocks  G,  whereby  A  and  B  are  sep- 
arated momentarily.  As  soon  as  the  cam  block  G  has  been  passed, 
a  spring  brings  the  two  contact  points  together  again.  Sta- 
tionary contact  A  is  connected  with  one  end  of  the  primary  wind- 
ing of  the  armature,  while  the  other  end  has  a  metallic  connec- 
tion with  the  armature  core;  or  in  other  words,  is  grounded. 


G 

FIG.  49.    Diagram  of  Circuit  Breaker. 

When  these  two  contact  points  are  suddenly  separated,  there 
is  a  tendency  for  the  current  to  continue  to  flow  across  the  gap, 
it  possessing  a  property  similar  to  the  inertia  of  matter.  This 
would  result  in  a  hot  spark  being  formed  between  the  two  con- 
tact points,  which  would  not  only  burn  the  points  away  rapidly, 
but  would  also  prevent  a  rapid  cessation  of  the  current. 

The  Condenser. — To  avoid  this,  a  condenser  is  used,  which  is 
built  into  the  magneto.  This  condenser  consists  of  two  sets  of 
tinfoil  sheets,  sheets  of  opposite  sets  alternating  with  each  other, 
and  being  separated  by  sheets  of  insulating  material.  All  the 
sheets  of  each  set  are  metallically  connected,  and  one  set  is  con- 
nected with  the  primary  winding,  while  the  other  set  is  grounded. 
These  condensers  are  capable  of  absorbing  an  electrical  charge, 
and  their  capacity  is  so  proportioned  that  they  will  take  up  the 
entire  charge  of  extra  current  produced  when  the  contact  points 


IGNITION  SYSTEMS  65 

of  the  circuit  breaker  separate — that  is,  the  extra  current  instead 
of  appearing  in  the  form  of  a  spark  across  the  gap,  passes  into 
the  condenser. 

Controlling  the  Point  of  Ignition. — The  magneto  armature  is 
positively  driven  from  the  motor  crankshaft  and  the  current  im- 
pulse in  the  armature  always  occurs  when  the  piston  is  in  a  cer- 
tain position.  Since  in  regular  operation  of  the  motor  the  charge 
is  ignited  just  an  instant  before  the  completion  of  the  compres- 
sion stroke,  the  magneto  armature  is  so  set  relative  to  the  engine 
crankshaft  that  the  maximum  induction  effect  occurs  at  this 
moment.  This  construction  is  termed  a  fixed  spark.  However, 
quite  a  few  users  demand  a  variable  spark;  or  in  other  words, 
to  vary  the  time  of  the  cycle  when  ignition  occurs.  In  order  to 
make  this  possible,  the  circuit-breaker  housing  F  is  so  arranged 
that  it  can  be  rocked  around  its  axis,  being  provided  with  a  lever 
arm  for  this  purpose,  which  is  connected  with  the  spark  lever  on 
the  steering  gear. 

In  the  Mea  magneto,  owing  to  its  construction,  the  circuit 
breaker  and  the  magnets  are  moved  around  their  axis  so  that  the 
armature  will  hold  its  relation  to  the  pole  pieces,  whether  ad- 
vanced or  retarded. 

An  Automatic  Control. — One  model  of  Eiseman  magneto  in- 
corporates an  automatic  spark  advance,  which  is  accomplished 
by  the  action  of  centrifugal  force  on  a  pair  of  weights  attached 
to  one  end  of  a  sleeve,  through  which  runs  the  shaft  of  the  mag- 
neto, and  hinged  at  the  other  end  of  the  armature.  Along  the 
armature  shaft  run  two  helicoidal  ridges,  which  engage  with  sim- 
ilarly shaped  splines  in  the  sleeve.  When  the  armature  is  rotated, 
the  weights  begin  to  spread  and  exert  a  longitudinal  pull  on  the 
sleeve,  which  in  turn  changes  the  position  of  the  armature  with 
reference  to  the  pole  pieces.  In  this  way  the  moment  of  the 
greatest  induction  is  advanced  or  retarded,  and  with  it  the 
breaker  in  the  primary  circuit. 

The  Distributor. — The  high-tension  current  is  distributed  to 
the  spark  plugs  in  the  following  manner:  One  end  of  the  sec- 
ondary winding  is  grounded  through  the  primary  winding,  since 
it  is  attached  to  one  end  of  the  primary,  the  other  end  of  which  is 
grounded.  The  other  end  of  the  secondary  generally  leads  to  the 
collector  ring,  from  which  the  current  is  taken  off  by  a  carbon 
brush.  From  here  the  current  is  carried  through  a  spring  con- 
tact conductor  to  a  distributor  on  the  magneto.  This  distributor 


66   MOTOE  TRUCK  DESIGN  AND  CONSTRUCTION 

consists  of  an  insulated  disc,  in  which  are  imbedded  on  the  inner 
side  one  central  contact  piece  and  four  or  six  sector-shaped  con- 
tact pieces,  the  number  depending  upon  the  number  of  cylinders 
on  the  engine.  This  distributor  also  comprises  a  shaft  which 
carries  a  gear  wheel  meshing  with  another  on  the  armature  shaft. 
The  reduction  between  these  gears  is  two  to  one,  so  that  the  arma- 
ture shaft  makes  two  turns.  The  large  gear  wheel  carries  a  brush 
holder,  containing  a  carbon  brush,  which  makes  contact  simul- 
taneously with  the  central  contact  piece  and  one  of  the  sector- 
shaped  contact  pieces,  which  are  connected  by  means  of  wiring 
or  cable  to  the  spark  plugs. 

A  magneto  must  be  so  designed  that  it  will  give  a  sufficiently 
hot  spark  at  a  comparatively  low  engine  speed.  This  ability  im- 
plies the  ability  of  generating  very  large  and  hot  sparks  and 
enormously  high  tensions  at  high  engine  speeds. 

The  Safety  Gap. — The  electromotive  force  generated  in  the 
secondary  winding  is  limited  to  the  size  of  the  spark  gap  of  the 
spark  plugs;  for,  as  soon  as  the  tension  reaches  a  point  sufficient 
to  jump  this  gap,  the  discharge  occurs  and  there  is  no  further 
increase  in  the  electromotive  force.  If,  by  chance,  the  gap  be- 
tween the  spark  plug  electrodes  become  large  enough  that  there 
is  no  chance  for  the  sparks  to  pass  in  the  ordinary  way,  the  elec- 
tromotive force  in  the  secondary  winding  might  build  up  to  such 
an  extent  as  to  puncture  the  insulation  of  the  winding  and  ruin 
the  armature.  To  avoid  this,  a  safety  gap  is  provided  in  which 
the  gap  is  larger  than  in  the  spark  plugs.  Under  ordinary  con- 
ditions, no  spark  will  pass  between  the  two  terminals  of  the  safety 
gap.  However,  should  the  condition  mentioned  above  arise,  a  dis- 
charge will  Occur  at  the  safety  gap,  preventing  the  electromotive 
force  from  rising  still  higher. 

Function  of  the  Switch. — In  order  to  stop  the  magneto  from 
producing  sparks,  when  it  is  desired  to  shut  down  the  motor,  a 
switch  is  provided.  One  terminal  of  the  switch  is  grounded  to 
the  engine  or  frame,  while  the  other  is  connected  to  a  binding 
post  on  the  circuit-breaker  housing.  This  binder  post  is,  in  turn, 
connected  with  the  contact  points  of  the  circuit  breaker.  When 
the  switch  is  closed,  the  current  generated  in  the  primary  wind- 
ing flows  to  the  contact  points  and  through  the  binding  post  and 
connecting  wire  to  the  switch,  whence  it  passes  through  a  wire 
to  the  frame  work  of  the  car  and  return  to  the  beginning  of  the 
primary  winding.  In  other  words,  the  switch  cuts  out  the  cir- 


IGNITION  SYSTEMS 


67 


cuit  breaker  and  the  primary  winding  is  short  circuited  all  the 
time,  so  that  the  opening  and  closing  of  the  contact  points  has  no 
effect. 

Summary  of  Independent  System. — Fig.  50  shows  the  path 
of  the  primary  circuit  originating  in  the  primary  winding  of  the 
armature.  It  flows  through  the  contact  breaker  screw  to  the  sta- 
tionary contact  point,  thence  across  to  the  movable  contact  point, 


SPARK  PLUGS 


—  PRIMARY  WINDING 
SECONDARY  WINDING 

—  -   FRAME 


iSAFETY  SPARK  GAP 

DISTRIBUTOR  PLATE 


»- 


V_.  _l L.. 


FIG.  50.     Path  of  Primary  Circuit,  Originating  in  the  Armature. 
Primary  Winding. 

from  where  it  is  led  through  the  contact  brush  in  the  framework 
of  the  magneto,  whence  it  returns  to  the  beginning  of  the  primary 
winding,  which  is  also  connected  or  grounded  to  the  frame.  The 
beginning  of  the  secondary  winding  is  connected  to  one  end  of 
the  primary  winding,  and*  since  one  end  of  the  primary  is 
grounded,  the  secondary  is  also  grounded  through  the  primary. 
The  other  end  of  the  secondary  winding  leads  to  the  insulated 
collector  ring,  from  which  the  current  is  taken  off  by  a  carbon 
contact  brush.  From  the  brush  holder  the  current  is  carried 
through  a  spring  contact  conductor  to  the  distributor,  from 
where  it  is  distributed  to  the  spark  plugs. 

Dual  Systems. — So  far  high-tension  magnetos  of  the  inde- 
pendent type  have  been  discussed.  However,  most  all  magneto 
makers  also  build  high-tension  magnetos,  which  provide  a  dual 
ignition  system,  using  a  battery  and  coil  with  one  set  of  spark 


68      MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


plugs.  Some  makers  use  the  magneto  breaker  for  the  battery  cur- 
rent, while  others  provide  a  separate  circuit  breaker  to  avoid  the 
possibility  of  both  systems  being  put  out  of  commission  by  an 
accident  affecting  only  one,  but  subsequently  extended  to  the 
other  on  account  of  its  close  relationship.  The  same  distributor 
is  used  for  both  systems. 

The  Coil.  —  The  battery  current  is  of  a  low  tension  and  con- 
nected with  a  two-point  switch  on  the  coil.  From  the  coil  the 
current  is  led  to  the  circuit  breaked,  and,  as  the  circuit  is  broken 


SWITCH  HANDLE  (CAN  BE  REMOVED) 


TO  THE    PLUGS 


-  HIGH  TENSION  CABLE  (/ 
—  LOW  TENSION  CABLE  (I 


%To%"ntieii) 


FIG.  51.     Wiring.     Diagram  of  Eiseman  Dual-Ignition  System. 

at  the  proper  moment,  a  very  high  voltage  is  induced  in  the  sec- 
ondary of  the  coil  or  transformer,  and  being  delivered  to  a  heavily 
insulated  cable,  is  conducted  to  the  central  carbon  brush  of  the 
distributor,  whence  it  is  delivered  to  the  spark  plugs  in  the  dif- 
ferent cylinders  in  correct  sequence. 

The  coil  has  a  primary  and  secondary  winding,  similar  to 
that  of  the  armature  of  the  magneto,  and  performs  the  same 
function  in  the  battery  circuit,  being  provided  with  a  separate 
condenser. 


IGNITION  SYSTEMS  69 

Fig.  51  is  a  wiring  diagram  of  the  Eiseman  dual  ignition  sys- 
tem. The  high  tension  is  led  from  the  collector  ring  of  the  mag- 
neto of  HM  and  led  to  TIM  on  the  coil,  thence  to  the  switch  H  on 
the  coil  and  to  H  on  the  magneto.  When  the  coil  handle  is 
shoved  over  to  the  battery  position,  several  operations  take  place 
in  the  switch  of  the  coil.  First,  the  primary  current,  emanating 
from  the  terminal  MA  of  the  magneto,  is  led  to  the  ground  or 
body  of  the  magneto,  and  this  prevents  it  from  generating  a  high- 
tension  current.  Second,  the  battery  current  is  allowed  to  flow 
in  the  coil  at  +  on  the  coil,  through  the  coil,  thence  to  R  on  the 
coil  to  R  on  the  magneto,  where  it  is  interrupted  by  a  circuit 
breaker,  thence  it  returns  to  the  battery  through  the  ground. 
When  it  is  desired  to  stop  the  motor,  the  coil  handle  is  moved  to 
the  off  position,  cutting  off  the  battery  current  and  the  magneto 
current  remains  short  circuited,  thus  eliminating  all  ignition. 

Operation  of  Switch. — But,  if  instead  of  leaving  the  handle  at 
"  off,"  it  is  quickly  shoved  from  "  Bat,"  to  "  Mag,"  without  ar- 
resting it  between  the  two,  the  motor  begins  to  run  on  the  mag- 
neto current.  In  this  case  the  battery  current  is  left  cut  off  as  in 
the  "  off  "  position,  while  the  connection,  which  in  both  the  other 
positions  has  led  the  primary  circuit  of  the  magneto  to  be  ground, 
is  broken,  with  the  result  that  this  current  is  diverted  to  the 
breaker  mechanism  on  the  armature  shaft,  thus  generating  in 
the  secondary  winding  of  the  magneto  the  high-tension  current 
led  to  the  spark  plug. 

The  same  distributor  is  used  for  the  battery  high-tension  cur- 
rent, for,  when  the  switch  is  on  "  Bat,"  there  is  a  connection 
made  between  the  end  of  the  coil's  secondary  winding  and  the 
terminal  H  on  the  coil,  which  sends  the  battery  current  over  the 
same  route  as  that  of  the  magneto. 

Before  the  motor  is  in  motion,  the  interrupter  R,  still  re- 
ferring to  Fig.  51,  cannot  operate,  and  this  makes  necessary  in- 
terruptions by  hand  with  a  starter  knob  when  starting  from  the 
seat  on  compression.  This  takes  the  place  momentarily  of  the 
circuit  breaker,  being  supplanted  by  the  latter  the  moment  the 
engine  turns  over. 

Low-tension  Magneto  and  Battery  Systems. — As  mentioned  in 
the  above,  all  systems  using  a  spark  plug  are  termed  high-tension 
systems;  however,  a  low-tension  magneto  may  be  used  with  a 
transformer  coil.  Eeference  was  made  to  the  instrument  having 
a  single  winding  on  its  armature  and  employing  a  step-up  coil 


70   MOTOE  TRUCK  DESIGN  AND  CONSTRUCTION 

with  a  primary  and  secondary  winding.  This  type,  termed  a 
high-tension  system,  although  a  low-tension  current  is  obtained 
from  the  instrument  itself.  However,  this  low-tension  current  is 
transformed  into  a  high-tension  by  the  coil. 

These  coils  are  similar  to  those  used  in  connection  with  bat- 
tery systems,  and  as  but  few  more  wires  are  necessary  to  use  a 
battery  current,  the  system  is  generally  of  the  dual  type,  making 
use  of  the  magneto  interrupter  and  distributor  for  both  magneto 
and  battery  current.  The  low-tension  magneto  is  sometimes  de- 
fined as  the  primary  armature  type,  as  it  incorporates  but  a  single 
or  primary  winding  in  the  magnetic  field. 

The  construction  of  a  low-tension  magneto  is  similar  to  that 
of  the  high-tension  type.  It  consists  of  permanent  magnets  of 
inverted  U-shape,  and  the  pole  pieces  bored  out  cylindrically, 
mounted  upon  a  non-metallic  base.  The  armature  is  also  of  H 
section,  carries  a  primary  winding  and  serves  to  form  a  bridge 
for  the  magnetic  flux  between  the  pole  pieces.  The  armature 
core  is  wrapped  with  primary  wire  until  the  slot  is  almost  filled. 
The  insulating  cloth  is  then  put  in  place  and  the  armature 
banded. 

A  low-voltage  current  is  furnished  by  the  magneto  armature 
to  the  primary  winding  of  the  coil,  while  a  secondary  winding  in 
the  coil  transforms  this  to  a  high  voltage. 

The  interrupter  and  distributor  are  similar  to  the  high-ten- 
sion type  and  perform  the  same  functions  in  the  system. 

The  main  constructive  difference  between  the  low  and  high- 
tension  types  is  that  the  former  has  but  one  winding  on  the  arma- 
ture, using  a  transformer  coil  to  raise  current  pressure  value, 
whereas  the  high-tension  type  has  a  secondary  winding  incor- 
porated in  the  armature. 

The  principle  of  a  rotating  armature  and  the  method  of  gen- 
erating current  in  the  magnetic  field  was  explained  previously. 
We  may  now  discuss  the  method  of  transforming  the  low -tension 
current  to  a  high  tension. 

Fig.  52  is  a  wiring  diagram  of  this  type,  with  external  trans- 
former coil.  It  will  be  noted  that  the  primary  winding  of  the 
transformer  is  so  connected  with  the  magneto  armature  winding 
that  it  completes  the  metallic  circuit  through  the  latter.  That  is, 
the  transformer  primary  is  in  series  with  the  armature  winding. 
The  breaker  points  are  separated  at  definite  intervals,  and  are  so 
connected  into  the  armature  and  transformer  primary  circuit 
that  a  direct  short  circuit  through  the  armature  winding  is 


IGNITION  SYSTEMS 


71 


caused  when  they  are  in  contact.     The  breaker  points  are  here 
said  to  be  connected  in  parallel  with  the  transformer  primary. 

As  the  induced  electric 
pressure  within  the  armature 
winding  rises  in  value,  due  to 
the  motion  of  the  armature 
in  the  magnetic  field,  it  flows 
through  the  circuit  formed 
by  the  armature  winding  and 
the  circuit  breaker  points  un- 
til the  instant  at  which  it  has 
attained  its  maximum  value, 
when  the  contact  points  are 
separated  and  the  direct  short 
circuit  broken.  When  this 
separation  of  the  points  oc- 
curs, the  induced  electric  pres- 
sure is  caused  to  enter  the 
transformer  primary  with 
great  suddenness  and  create 
lines  of  force  through  the 
transformer  windings  with 
extreme  rapidity.  This  entry 
by  the  current  and  consequent 
creation  of  lines  of  force 
causes  the  lines  to  cut  the  sec- 
ondary winding  during  the 
formation  of  the  magnetic 
field  about  the  transformer, 
and  this  cutting  induces  an 
Ex  electrical  pressure  within  the 
secondary. 

Of  course  with  this  sys- 
tem the  armature  of  the  magneto  is  positively  driven  from  the 
engine  by  gears,  so  that  the  points  of  maximum  pressure  induc- 
tion in  the  armature  winding  may  coincide  with  the  instants  at 
which  ignition  sparks  are  desired  within  the  engine  cylinders. 
Such  a  single  transformer  with  a  single  breaker  is  employed  and 
all  the  current  for  ignition  is  generated  therein;  it  is  necessary 
that  some  means  be  fitted  for  the  distribution  and  consecutive 
connections  of  the  transformer  secondary  with  the  proper  spark 


FIG.  52.       Wiring-     Diagram     for 
Low-Tension     Magneto     with 
ternal  Transformer  Coil. 


72   MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


plugs  in  the  cylinders.  This  distribution  is  accomplished  by  a 
distributor,  also  made  an  integral  part  of  the  magneto,  and 
driven  positively  and  in  a  definite  relationship  with  the  circuit 
breaker  as  in  the  high-tension  type. 

Again  referring  to  Fig.  52,  it  is  seen  that  the  ends  of  the  trans- 
former secondary  winding  are  connected,  for  the  completion  of 
its  circuit  through  the  spark  plugs,  one  to  engine  frame,  or  in 
other  words,  one  end  is  grounded  and  the  other  the  central  car- 
bon brush  holder  of  the  distributor. 

This  distributor  is  of  the  same  construction  as  in  the  high- 
tension  system,  so  that  the  high-tension  current  induced  in  the 
secondary  winding  will  be  forced  to  follow  the  path  selected  for 
it,  depending  upon  the  position  of  the  carbon  brush  of  the  dis- 
tributor. In  this  illustration  the  heavy  lines  illustrate  the  pri- 
mary circuit  and  the  light  lines  the  secondary  circuit. 

Most  coils  in  use  at  the  present  writing  are  of  the  non-vibrat- 
ing type,  the  trembler  type  of  box  coil  having  been  discarded 
long  ago,  and  the  interrupter  is  now  operated  mechanically  in- 
stead of  electrically. 

These  non- vibrating  or  transformer  coils,  as  they  are  termed, 
are  made  in  various  styles,  and  sometimes  incorporate  the  switch 
and  a  push  button  for  starting  on  the  spark. 

The  most  popular  type 
is  the  tube  coil  with 
switch,  which  can  be 
mounted  on  the  dash  un- 
der the  hood  with  switch 
on  the  outside,  within 
reach  of  the  operator.  In 
some  cases  the  coil  is  made 
separately  and  mounted 
under  the  hood,  while  the 
switch  has  the  usual  posi- 
tion on  the  dash. 

Fig.  53  illustrates  the  wound  core  of  a  transformer  coil,  com- 
plete with  condenser  casing.  These  coils  are  mounted  in  a  tubular 
case  provided  with  front  and  rear  end  plates.  The  front  plate 
carries  the  switch  handle  and  push  button,  while  the  rear  end 
carries  the  terminals  and  is  enclosed  by  a  cover,  so  that  the  coil 
and  connections  are  thoroughly  protected. 

The  push  button  is  used  for  producing  a  spark  in  the  cylinder 
by  interrupting  the  primary  circuit  leading  from  the  battery. 


/CONDENSER 


'INSULATED 
WINDINGS 


FIG.  53.     Transformer    Coil. 


IGNITION  SYSTEMS 


73 


taking  the  place  momentarily  of  the  breaker  on  the  magneto. 
Some  coils  are  fitted  with  a  ratchet  mechanism  giving  a  series 
of  sparks  in  the  cylinder.  Some  are  also  provided  with  a  lock 
and  key,  so  that  the  switch  may  be  locked  in  the  "  off  "  position, 
preventing  the  unauthorized  use  of  the  truck. 

The  action  of  the  switch  was  explained  previously  in  connec- 
tion with  the  dual  system,  and  requires  no  further  discussion. 


FIG.  54.     Wiring  Diagram  of  an  Induction  Coil  and  the  Other  Components 
of  a  Battery  System. 

The  battery  system,  providing  a  jump  spark,  was  extensively 
used  before  the  magneto  became  so  popular.  This  system  re- 
quires a  series  of  dry  cells  or  a  .storage  battery,  affording  a  low- 
tension  current  and  a  timer,  the  current  being  stepped-up  to  a 
high-tension  by  induction.  The  principle  of  self-induction  is  as 
follows : 

A  current  flowing  through  a  coil  of  wire  will  set  up  a  mag- 
netic field  in  the  surrounding  space,  but  when  the  current  is 
stopped  the  magnetic  field  will  stop.  The  effect  of  the  stoppage 
of  the  flow  of  current  in  this  coil  is  the  same  as  that  due  to  the 
change  of  position  of  the  wire  coil  in  a  magnetic  field,  so  that 
when  the  current  is  stopped  there  will  be  a  current  induced  in  the 


74   MOTOE  TEUCK  DESIGN  AND  CONSTEUCTION 

coil.  The  result  is  that  when  the  circuit  is  broken  to  stop  the  cur- 
rent, the  decrease  in  the  current  adds  momentarily  to  the  electro- 
motive action  in  the  circuit  and  a  visible  spark,  or  even  an  arc, 
is  formed  at  the  break. 

Fig.  54  makes  clear  the  principles  of  an  induction  coil,  show- 
ing the  primary  and  secondary  circuits  and  the  other  components 
of  the  system. 

The  primary  and  secondary  windings  are  identical  with  those 
of  the  compound  armature,  or  high-tension  magneto,  the  former 
consisting  of  a  small  number  of  turns  of  coarse  insulated  wire, 
while  the  latter  is  a  very  fine  silk  insulated  wire,  and  the  number 
of  turns  greatly  exceeds  those  of  the  primary  winding.  In  this 
system  no  mechanically  operated  interrupter  is  used  for  breaking 
the  primary  circuit,  this  being  accomplished  by  a  device  for 
automatically  and  rapidly  making  and  breaking  the  circuit. 

The  device  is  known  as  a  vibrator  or  trembler,  as  it  is  some- 
times termed,  and  consists  of  an  iron  disc  of  approximately  the 
same  diameter  as  the  core  of  the  coil,  attached  to  flat  spring  and 
a  platinum  point  located  above  the  disc.  An  adjusting  screw 
mounted  above  the  disc  carries  another  platinum  point.  These 
points  are  so  situated  on  the  coil  that  they  make  contact  with  each 
other.  When  these  two  points  are  in  contact,  the  primary  circuit 
is  closed. 

The  automatic  action  of  this  vibrator  is  as  follows:  The  cur- 
rent flowing  through  the  primary  circuit  of  the  coil  makes  an 
electromagnet  of  the  core,  which  attracts  the  iron  disc  attached  to 
the  vibrator  spring,  causing  the  points  to  separate.  As  the  cur- 
rent is  interrupted  by  the  separation  of  these  points,  the  core 
ceases  to  be  an  electromagnet,  since  no  current  is  flowing  through 
it  and  the  disc  is  no  longer  attracted  permitting  the  points  to 
make  contact  and  again  complete  the  primary  circuit.  This 
action  continues  as  long  as  the  current  flows  and  is  interrupted 
in  the  primary  circuit.  By  varying  the  adjustment  of  the  ad- 
justing screws  the  number  of  sparks  in  a  given  time  are  varied, 
as  is  also  the  strength  of  the  individual  sparks. 

To  prevent  prolonging  the  magnetization  of  the  core  beyond 
the  desired  limit,  a  condenser  is  connected  with  the  contact 
points  to  absorb  the  surplus  current  induced  in  the  primary  cir- 
cuit, due  to  the  breaking  of  the  circuit.  In  other  words,  when 
the  points  are  in  contact,  the  condenser  is  short  circuited,  but 
when  the  circuit  is  broken  the  induced  current,  instead  of  jump- 
ing across  the  gap,  passes  into  the  condenser,  and  as  the  circuit  is 


IGNITION  SYSTEMS 


75 


again  completed  it  passes  out  again  and  into  the  circuit.  A  com- 
mutator, or  timer,  is  used  to  determine  the  exact  time  in  the  cycle 
of  the  engine  at  which  ignition  occurs. 

The  diagram  shown  herewith  represents  a  single-cylinder  sys- 
tem, while  multi-cylinder  engines  require  a  coil  for  each  cylinder, 
but  the  battery  current  passing  into  the  primary  winding  of  the 
coils  is  controlled  by  a  single  switch.  The  coil  units  are  incor- 
porated in  a  box  or  housing  which  is  mounted  on  the  dash  board, 
with  a  removable  cover,  so  that  any  coil  may  be  adjusted.  As 
each  coil  is  a  separate  unit,  they  may  be  so  constructed  that  they 
may  easily  be  replaced  should  they  become  defective,  without 
disturbing  any  connections. 

In  every  high-tension  battery  system  a  device  is  required  for 
opening  and  closing  the  primary  circuit  at  the  proper  instant, 
with  respect  to  the  cycle  of  the  engine,  and  the  position  of  the 
piston  in  the  cylinder.  This  device  is  known  as  the  timer,  be- 
cause it  determines  the  exact  time  in  the  cycle  of  the  engine  at 
which  ignition  occurs  and  permits  of  varying  this  point  at  will 
while  the  engine  is  in  operation.  It  is  positively  driven  by  gears 
from  the  motor  either  direct  or  through  an  auxiliary  shaft  from 
the  cam  shaft.  This  timer 
(Fig.  55)  consists  of  a  hous- 
ing containing  a  roller  and 
arm  members  so  mounted  upon 
the  driving  shaft  that  the 
roller  and  arm  members  may 
rotate,  while  the  housing  is 
held  stationary  by  means  of  a 
rod  or  lever,  which  may  be 
moved  in  either  direction  to 
advance  or  retard  the  spark. 
Within  the  housing  is  a  fiber 
ring  in  which  are  mounted 
metal  contact  segments,  the 
surfaces  of  which  are  flush 
with  the  fiber. 

These  segments  are  held  in  position  by  screw  bolts  which  pass 
through  the  fiber  ring  and  housing,  but  are  insulated  from  the 
latter.  These  screw  bolts  are  provided  with  thumb  nuts  and  ter- 
minals to  which  is  secured  a  primary  wire,  which  in  turn  is  con- 
nected to  the  primary  terminal  of  the  induction  coil. 


FIG.  55.     Timer  for  Battery  System. 


76   MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

The  operation  of  the  timer  is  as  follows :  The  shaft  actuating 
the  roller  is  metal,  and  one  lead  from  the  battery  is  connected  to 
the  frame,  or  other  metal  part,  and  the  current  is  conducted  from 
its  source  to  the  metal  segment.  As  the  roller  makes  contact  with 
the  segment  in  the  fiber  ring,  the  circuit  is  closed  and  the  current 
flows  through  the  roller  frame  and  primary  wire  back  to  its  orig- 
inal source.  As  the  roller  contact  with  the  segment  is  broken,  the 
primary  current  in  the  coil  is  established  and  broken  as  pre- 
viously described,  being  built  up  in  the  secondary  winding,  and 
a  spark  produced  at  the  gap  of  the  spark  plug  electrodes. 

The  vibrator  coil  system  has  its  disadvantages,  having  sev- 
eral primary  contacts,  sliding  or  rolling  contacts  in  the  timer, 
and  a  delicate,  magnetic  interrupter.  To  overcome  these  faults, 
igniters  were  introduced  which  combine  a  mechanical  interrupter 
with  a  high-tension  distributor.  The  induction  coil  is  replaced 
by  a  transformer  coil,  as  used  with  the  primary  armature  type  of 
magneto.  With  the  igniter  system  but  one  primary  contact  is 
necessary  and  the  circuit  is  made  and  broken  positively  by  me- 
chanical means. 

The  contact  points  are  generally  so  constructed  that  they 
may  be  adjusted  from  the  outside  without  dismantling  the  unit. 

Directly  above  the  contact  maker  is  located  the  high-tension 
distributor.  Its  construction  is  similar  to  the  high-tension  mag- 
neto distributor,  using  a  central  contact  brush  and  segments 
located  radially  which  are  connected  with  the  spark  plugs  of  the 
motor. 

The  advantages  of  this  system  over  the  vibrator  coil  system 
are  two-fold.  As  there  is  only  one  set  of  wearing  parts,  whatever 
wear  occurs  will  affect  the  timing  of  all  cylinders  equally  and 
subsequently  a  perfect  relationship  is  maintained  at  all  times. 
Again  the  character  of  the  spark  in  all  cylinders  must  be  identical. 

Fig.  56  indicates  the  path  of  the  current  in  the  igniter  system, 
passing  from  the  battery  to  the  switch  on  'the  coil,  thence  to  the 
interrupter,  from  where  it  is  led  to  the  coil  and  stepped-up  to  a 
high  pressure.  From  the  coil  it  passes  through  a  conductor  to 
the  central  contact  of  the  distributor  and  is  distributed  to  the 
cylinders  in  proper  sequence. 

Either  the  vibrator  and  timer  system,  or  the  igniter  system, 
may  be  used  in  connection  with  either  the  primary  or  compound 
armature  magneto,  thus  forming  two  separate  systems  of  ignition, 
with  either  one  or  two  sets  of  spark  plugs.  With  the  former  type 
the  magneto  distributor  is  used  for  both  systems,  while  a  vibrator 


IGNITION  SYSTEMS 


77 


and  a  transformer  coil  are  mounted  together  and  controlled  by  a 
single  switch.  When  the  compound  armature  magneto  is  used, 
but  one  coil  is  necessary  for  the  battery  system.  The  above  is 
also  true  of  the  igniter  and  transformed  coil,  excepting,  of  course, 
that  but  one  coil  is  necessary  for  either  type  of  magneto. 


To  Coil- 


FIG.  56.     Indicating  the  Path  of  Current  in  an  Igniter  System. 

Inductor  Magnetos. — The  magnetos  described  previously,  gen- 
erating either  high  or  low-tension  current,  were  built  on  the  prin- 
ciple of  placing  the  winding  or  windings  on  the  armature  core, 
so  as  to  rotate  in  unison  with  the  armature. 

The  inductor  type  of  magneto  differs  from  the  above,  in  that 
the  windings  are  stationary  within  the  magnetic  field  of  the  mag- 
neto and  the  armature  is  replaced  by  inductors  which  revolve, 
being  attached  to  a  shaft.  In  fact,  these  are  the  distinguishing 
features  of  this  type  of  magneto.  In  other  words,  a  stationary 
winding  is  used  and  mechanical  energy  is  transformed  into  elec- 
trical energy  through  a  distinctive  principle  known  as  induction. 

This  inductor  type,  like  the  primary  and  compound  arma- 
ture types,  consists  of  permanent  inverted  U-magnets  and  pole 
pieces  which  form  the  magnetic  field,  mounted  upon  a  non- 
metallic  base.  The  winding  or  windings  may  be  arranged  for 


78      MOTOE  TEUCK  DESIGN  AND  CONSTEUCTION 

either  a  high  or  low-tension  current  and  may  either  be  placed  in 
the  magnetic  field  or  at  the  rear  end  of  the  magneto. 

The  armature  is  replaced  by  inductors,  mounted  upon  a  shaft, 
this  unit  being  termed  the  rotor  shaft.  The  inductors  are 
in  some  cases  fan-shaped.  The  Eemy  inductor  shaft,  which  is 

of  this  type,  is  illustrated 
in  Fig.  57.  It  is  made  of 
laminated  steel,  claim  being 
made  for  a  better  magnetic 
circuit  with  this  construc- 
ts! wHif  tion.  Each  lamination  is 

Ja*^S'  ^^^^^Ht^^^^MV^KlB^te6» 

xf  given  an  insulated  coating 

on  one  side,  the  object  of 
this  being  to  eliminate  eddy 
FIG.  57.  Eemy  Induction  Shaft.  currents  and  to  reduce  heat 

losses. 

The  circuit  breaker,  or  interrupter,  is  also  used  to  open  and 
close  the  primary  circuit  at  the  proper  time,  while  the  distributor 
is  also  resorted  to  to  distribute  the  high-tension  current  to  the 
proper  cylinders.  In  fact,  this  type  of  magneto  incorporates  all 
the  principal  parts  mentioned  in  connection  with  the  previous 
types,  such  as  the  condenser,  safety  spark  gap  and  switch. 

The  functions  performed  by  these  units  are  identical  with 
those  described  previously.  As  mentioned  above,  the  principal 
difference  of  this  instrument  over  the  others,  lies  in  the  method 
of  generating  the  current. 

Previously  the  method  of  magnetizing  a  bar  was  described  in 
connection  with  the  induction  coil,  and  we  may  now  investigate 
the  method  of  utilizing  this  magnetism  to  produce  electrical 
currents. 

In  a  coil,  an  electrical  current  will  be  said  to  be  flowing  in  the 
coil,  meaning  that  it  passes  in  the  wire.  Magnetic  flux,  however, 
will  be  said  to  pass  through  the  core  in  either  direction,  the  core 
serving  as  a  path  to  direct  the  magnetism  through  the  coil.  An 
electrical  action  is  produced  by  the  action  of  the  magnetism  in 
the  core  only  when  the  strength  of  the  magnetism  varies,  that  is, 
when  it  increases  or  decreases.  When  this  is  the  case  an  electro- 
motive force  is  induced  in  the  winding  and,  the  more  rapid  the 
variation  of  the  magnetism,  the  greater  the  induced  electro- 
motive force.  Even  if  the  core  is  traversed  by  a  large  amount  of 
magnetism,  it  has  no  effect  on  the  winding,  as  long  as  its  value  is 


IGNITION  SYSTEMS 


79 


unchanged.  Electromotive  force  tends  to  produce  an  electric  cur- 
rent and  if  the  circuit  is  closed  it  actually  does  produce  a  current. 
The  electromotive  force  produced  in  a  single  turn  of  winding 
is  proportional  to  the  rate  at  which  the  magnetism  through  that 
turn  varies.  A  winding  of  several  turns  may  be  regarded  as  sev- 
eral windings  of  one  turn,  connected  in  series,  so  that  to  obtain  a 
high  induced  electromotive  force,  a  winding  of  several  turns  is 
used,  just  as  several  dry  cells  are  connected  in  series  to  obtain  a 
higher  electromotive  force  from  that  obtained  from  a  single  cell. 


FIG.  58.     Positions   of  Inductors  and  their   Shaft. 

In  Fig.  58  are  shown  various  positions  of  the  inductors  and 
their  shaft.  The  upper  view  depicts  the  magneto  with  end  plates 
removed,  and  the  lower  view  represents  a  section  of  the  upper 
view. 

The  stationary  winding  is  securely  held  in  place  by  the  pres- 
sure of  the  pole  pieces  against  it  and  by  brass  strips  which  have 
been  omitted  to  simplify  the  illustration.  The  rear  inductor, 
which  is  located  to  the  rear  of  the  winding,  is  indicated  by  dotted 
lines  in  the  upper  views.  The  inductors  and  core  are  secured  to 
the  shaft  and  rotate  with  it,  constituting  the  only  moving  parts 
shown. 

In  order  to  form  a  path  for  the  magnetic  flux  it  is  merely  nec- 
essary to  have  a  mass  of  iron  joining  the  pole  pieces,  this  being 


80   MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

provided  by  the  inductors,  core  and  their  shaft.  The  arrows 
show  the  path  of  the  magnetism  through  the  revolving  parts. 

In  the  position  J.,  the  front  inductor  is  adjacent  to  the  pole 
piece  N)  the  rear  inductor  is  adjacent  to  the  pole  piece  $,  and  the 
path  is  formed  by  the  inductor  shaft.  When  the  cross-section  of 
the  inductor  shaft  is  not  great  enough  to  carry  all  the  flux,  a 
core  must  be  added  to  carry  part  of  it.  The  magnetism,  there- 
fore, in  position  J.,  passes  from  the  pole  piece  N,  to  the  front  in- 
ductor, through  the  core  and  shaft  to  the  rear  inductor,  thence  to 
the  pole  piece  S.  The  magnetism  through  the  winding  is  from 
the  front  to  the  back. 

At  B,  the  inductors  are  so  located  that  each  forms  a  path  be- 
tween pole  pieces  N  and  $,  and  the  magnetism  passes  between 
the  pole  pieces  without  any  of  it  passing  through  the  winding. 

At  6y,  the  conditions  are  similar  to  those  at  J.,  but  the  front 
inductor  is  adjacent  to  the  pole  piece  S  and  the  rear  one  adjacent 
to  the  pole  piece  N,  causing  the  magnetism  to  pass  through  the 
winding  from  back  to  front,  which  is  opposite  to  the  direction 
which  it  had  in  position  A. 

Position  D  is  similar  to  B,  except  that  the  front  inductor  is 
downward  and  the  rear  inductor  upward.  In  this  position  no 
magnetism  passes  through  the  winding.  From  the  above  it  can 
be  seen  that  the  magnetism  passing  through  the  winding  is  con- 
tinually varying,  thereby  inducing  in  the  winding  an  electro- 
motive force. 

As  the  inductors  approach  position  J.,  the  magnetism  through 
the  winding  is  increasing  and  as  they  leave  that  position  the  mag- 
netism begins  to  decrease,  without  changing  its  direction.  The 
direction  of  the  induced  electromotive  force  is  reversed  as  the  in- 
ductors pass  through  position  J.,  and  is  again  reversed  when  they 
pass  through  position  C.  As  the  inductors  approach  position  B, 
the  magnetism  through  the  winding  is  from  front  to  back  and 
decreasing,  but  after  they  have  passed  this  position,  it  is  from 
back  to  front  and  increasing,  resulting  in  no  reversal  of  the  elec- 
tromotive force.  This  is  also  true  of  position  D. 

Although  the  current  from  an  inductor  magneto  may  be  util- 
ized in  the  same  manner  as  that  from  any  other  alternating  cur- 
rent magneto,  the  above  sets  forth  the  conditions  existing  in  the 
Remy  magneto.  This  instrument  generates  a  low-tension  current 
and  requires  an  outside  coil  to  step  up  the  current  to  the  high 
potential  required  at  the  spark  plugs. 


IGNITION  SYSTEMS 


81 


FIG.  59.     K.W.  Inductor  Shaft. 


In  the  K.W.  inductor  type  of  magneto  (Figs.  59  and  60) 
there  are  four  inductors  as  illustrated  made  of  soft  iron  lamina- 
tions. Two  of  these  inductors  are  placed  180  degrees  to  each 
other  and  the  other  two  in 
a  plane  at  right  angles. 

The  windings,  which  are 
concentric  with  the  in- 
ductor shafts  are  mounted 
between  the  inductors  and 
stand  absolutely  still.  The 
inductors  collect  the  mag- 
netism from  one  pole  piece 
and  conduct  it  through  the 
center  of  the  windings  to 
the  opposite  pole  piece.  The 
primary  winding  is  sur- 
rounded by  the  secondary 
winding.  The  primary  cur- 
rent passes  through  the  cir- 
cuit breaker  and  at  the  moment  of  interruption  a  powerful  surge 
of  current  is  generated  in  the  secondary  winding,  which  is  dis- 
tributed to  the  spark  plugs,  thus  producing  a  high-tension  current 
without  the  aid  of  external  coils.  This  is  one  type  of  inductor 
magneto  generating  a  high-tension  current.  The  Pittsfield  mag- 
neto (Fig.  61)  offers  an- 
other example  of  a  high- 
tension  inductor  type  mag- 
neto; however,  it  differs 
materially  from  the  above. 
The  usual  primary  and  sec- 
ondary windings  are  used, 
however,  they  are  not  incor- 
porated with  the  inductor 
shaft,  but  are  located  at  the 

FIG.  60.     K.W.  High-Tension  Inductor      rear  °f  the  magneto. 

Magneto.  The   three    illustrations 

show  a  longitudinal  section 

through  the  entire  instrument,  cross  section  through  the  magneto 
and  pole  pieces  and  end  view  of  the  interrupter. 

The  magnetic  field  contains  four  poles,  two   (4A)   of  which 
are  the  poles  of  the  permanent  magnet  as  illustrated,  the  other 
7 


82   MOTOE  TRUCK  DESIGN  AND  CONSTRUCTION 

two  poles  (4)  and  the  iron  core  (5)  of  the  coil  compose  the  field. 
The  rotation  of  the  inductor  shaft  (1)  generates  in  the  windings 
of  the  coil  (6)  an  alternating  current  which  attains  a  maximum 
four  times  during  each  revolution  of  the  inductor  shaft,  which 
means,  that  for  each  90  degrees  rotation  of  the  inductor  shaft, 
ignition  may  be  obtained.  One  end  of  the  primary  winding  is 


23 


FIG.  61.     Longitudinal  Sectional,  Cross-Section  and  End  Views  of  Pitts- 
field  Magneto. 

connected  to  the  field  by  a  contact  (8)  and  its  other  end  is  at- 
tached to  a  contact  block  (9)  which  is  screwed  on  the  field  and 
insulated  by  a  hard  rubber  bushing  and  plate.  Connection  from 
this  plate  to  platinum  contact  block  (9)  and  screw  is  made  by  a 
brass  contact  strip.  The  latter  is  insulated  from  the  interrupter 
plate  (11),  which  is  in  metallic  connection  with  the  field  or 
ground. 

The  platinum  screw  (IS)  on  the  interrupter  lever  (12)  is  held 
against  the  platinum  screw  (1)  in  the  insulated  block  by  means 
of  a  spring  (H).  The  current  generated  in  the  primary  winding 
is  therefore  short  circuited  as  long  as  the  two  platinum  screws 
are  in  contact. 

The  primary  current  is  interrupted  when  the  core  (15)  actu- 
ates the  lever  (12)  separating  the  platinum  points.  A  condenser 
(16)  protected  by  a  housing  (17)  is  connected  in  parallel  to  the 
interruption  of  the  platinum  points.  One  end  of  the  secondary 
winding  is  connected  to  one  end  of  the  primary  winding  and 
the  other  is  led  to  a  conductor  by  means  of  a  metal  bridge  (19). 
The  secondary  current  is  led  from  this  bridge  member  to  the  dis- 
tributor (23)  by  means  of  insulated  conductors  (18),  which  are 
connected  by  means  of  a  carbon  brush  and  spring.  In  the  dis- 
tributor plate  (23)  are  socket  inserts  connected  to  distributing 


IGNITION  SYSTEMS  83 

inserts  which  take  the  high-tension  current  from  the  revolving 
conductor  (21}  in  proper  rotation  and  from  socket  inserts  in  the 
distributor  plate  (23)  cables  are  connected  to  the  spark  plugs  in 
the  cylinders. 

The  safety  spark  gap  consists  of  a  short  pointed  brass  rod 
set  on  the  metal  bridge  (19)  connecting  the  high-tension  terminal 
(26)  on  the  coil  (6)  with  the  high-tension  conductor  bar  (18), 
and  should  there  be  any  interference  with  the  circuit  normally 
provided  through  the  spark  plugs,  the  safety  gap  provides  a  point 
of  discharge. 

The  timing  of  the  spark  is  generally  accomplished  by  opening 
the  interrupter  earlier  or  later,  and  with  the  unavoidable  result 
that  if  the  position  of  the  pole  pieces  in  the  magnetic  field  re- 
mains stationary,  the  relative  position  of  inductor  shaft  and  field 
at  the  moment  of  the  break  must  vary.  The  quality  of  the  spark, 
or,  in  other  words,  the  heat  value,  depends  among  other  factors 
upon  the  particular  position  of  the  inductors  in  relation  to  the 
field  poles  at  the  moment  the  spark  is  produced. 

The  changing  of  the  timing  is  effected  in  the  Pittsfield  mag- 
neto in  a  unique  way.  The  results  obtained  are  ideal  in  that  the 
same  efficient  spark  is  obtained,  when  the  spark  is  either  ad- 
vanced, retarded  or  in  any  intermediate  position.  This  is  accom- 
plished by  means  of  a  four-segment  sleeve  (no.  27),  one  for  each 
pole  of  the  machine,  which  sleeve  is  fitted  with  a  lever  with  which 
the  sleeve,  with  interrupter,  can  be  advanced  or  retarded,  giving 
early  or  late  ignition. 

The  inductor  type  of  magneto  is  also  made  in  the  dual  type; 
in  fact,  in  the  Remy,  the  same  transformer  coil,  interrupter  and 
distributor  as  is  used  for  the  magneto  current.  With  the  K.W. 
it  is  necessary  to  employ  an  external  coil. 

The  Pittsfield  dual  system  is  somewhat  different  from  the 
other  types  explained,  and  owing  to  the  unique  construction  it 
is  very  simple.  It  does  away  with  the  high-tension  coil  and  wires 
from  the  magneto  to  the  switch,  the  dual  system  being  self- 
contained. 

The  design  and  constructional  details  of  the  dual  machine 
differ  from  the  independent  type,  as  previously  described,  by 
insulating  both  ends  of  the  primary  circuit  instead  of  one  end. 
One  end  of  the  primary  winding  is  connected  to  the  interrupter 
as  in  the  independent  type,  the  other  to  the  lever  of  a  specially 
constructed  switch,  so  that  when  the  switch  lever  is  on  the  side 


84    '  MOTOE  TKUCK  DESIGN  AND  CONSTRUCTION 

marked  "  Magneto,"  this  primary  lead  is  grounded,  allowing  the 
magneto  to  run  as  a  straight  high-tension  machine.  When  the 
lever  is  thrown  to  the  battery  side  of  the  switch  the  primary  lead 
is  then  connected  to  the  batteries,  thus  permitting  the  primary 
and  secondary  windings  of  the  magneto  to  be  used  for  either 
current. 


CHAPTER  VI 

GOVERNORS  AND  SPEED-CONTROLLING  DEVICES 

COMMERCIAL  car  manufacturers  and  users  are  aware  of  the 
attendant  results  of  high  speeds  and  heavy  loads  over  rough 
roads,  so  that  at  the  present  time  this  subject  should  be  of  con- 
siderable interest  to  those  operating  commercial  cars. 

The  most  practical  means  of  obviating  this  excessive  speed 
seems  to  be  through  the  use  of  a  governor,  which  should  be  sealed 
so  that  it  cannot  be  tampered  with. 

This  governor  consists  of  a  mechanical  speed-measuring  de- 
vice so  connected  to  the  engine  throttle  as  to  cut  off  the  intake 
when  the  speed  exceeds  a  predetermined  maximum.  It  was  orig- 
inally inherited  from  steam  engine  practice.  However,  lately, 
considerable  improvements  have  been  made  in  this  device  so  as  to 
make  it  more  adaptable  and  efficient. 

There  are  four  methods  of  regulating  the  speed  of  the  motor, 
as  follows:  (1)  By  holding  the  exhaust  valve  open  or  the  intake 
closed,  (2)  by  the  spark,  (3)  by  changing  the  quality  of  the  mix- 
ture entering  the  cylinder,  (4)  by  changing  the  quantity  of  the 
mixture  entering  the  cylinder. 

The  method  of  regulating  the  motor  speed  through  connecting 
the  governor  to  the  exhaust  valves  in  such  a  way  that  these  valves 
may  be  held  open,  and  thereby  retard  the  speed  of  the  motors,  or 
by  connecting  to  the  intake  valves  in  such  a  way  that  they  may 
be  held  closed,  has  been  discarded  long  ago. 

The  Dedion  Bouton  method  of  regulating  the  motor  speed 
through  connecting  the  governor  in  such  a  way  that  it  will  open 
and  close  the  electrical  circuit,  has  also  been  discarded.  This 
also  applies  to  the  method  of  changing  the  quality  of  the  mixture 
entering  the  cylinders. 

One  method  of  governing  the  speed  of  the  motor  is  by  con- 
necting the  governor  to  a  butterfly  valve  in  the  intake  manifold, 
which  reduces  the  quantity  of  the  mixture  entering  the  cylinder 
but  does  not  in  any  way  reduce  the  quality.  The  butterfly  valve 
merely  changes  the  volume  of  gas  and  allows  the  motor  to  get 
the  proper  mixture  under  any  speed  up  to  the  setting  of  the 
governor. 

85 


86      MOTOE  TRUCK  DESIGN  AND  CONSTRUCTION 

The  revolving  ball,  or  more  properly  the  centrifugal  prin- 
ciple, is  that  generally  employed.  There  are  many  variations  of 
this  construction  and  few  that  operate  on  different  principles,  but 
all  are  alike  in  fundamentals. 

The  hydraulic  principle  is  also  used  by  some.  In  this  type, 
as  the  motor  speed  raises  the  pressure  against  a  diaphragm  con- 
nected with  a  plunger-head  acting  on  the  throttle  spring.  This 
action  overcomes  the  resistance  of  the  spring  and  closes  the 
throttle.  This  type  may  either  be  built  in  a  unit  with  the  pump 
or  connected  to  it. 

There  is  also  the  automatic  type  which  regulates  the  motor 
speed  by  governing  the  velocity  of  the  incoming  gases. 

There  are  two  methods  of  drive  for  the  centrifugal  type  of 
governor.  The  usual  method  is  direct  from  the  engine,  either 
through  an  auxiliary  shaft,  or  by  building  the  governor  into  the 
cam-shaft  gear.  With  this  method  the  speed  of  the  governor  is 
always  proportioned  to  the  speed  of  the  motor. 

Lately  governors  are  being  introduced  which  are  driven  from 
some  part  of  the  chassis  and  whose  speed  is  proportioned  to  the 
speed  of  the  vehicle  instead  of  the  motor. 

In  the  former  case  the  governor  acts  only  on  the  motor  and 
converts  it  into  practically  a  constant  speed  motor.  In  changing 
speeds  the  allowed  speed  of  the  motor  is  in  no  wise  altered. 

The  governor  is  generaly  set  at  a  maximum  speed  correspond- 
ing to  the  maximum  car  speed  at  which  the  car  is  to  operate  on 
high  gear,  and  when  it  is  running  in  second  speed  the  effect  of 
the  governor  on  the  motor  does  not  change  in  any  way.  This 
second  speed  might  correspond  to  12  m.p.h.,  and  the  low  speed  to 
6  m.p.h.,  thus  limiting  the  motor  speed  on  the  lower  gears,  hence 
the  power  of  the  motor.  This  would  be  quite  noticeable  if  the  car 
was  operated  over  a  long  stretch  of  bad  road  or  in  deep  sand. 
The  power  output  of  the  engine  is  dependent  upon  its  speed  and 
although  it  may  be  pulling  hard  on  a  wide  open  throttle,  it  is  not 
developing  its  full  power,  for  not  enough  power  units  are  re- 
leased from  the  fuel,  owing  to  the  limited  speed.  The  maximum 
safe  motor  speed  may  be  far  above  the  speed  permitted  by  gov- 
ernor for  a  given  car  speed. 

These  defects  c  have  caused  engineers  to  investigate  other 
methods  of  governor  drives  and  has  resulted  in  the  introduction 
of  a  transmission  jack  shaft  or  front-wheel  drive,  on  the  theory 
that  the  speed  of  the  motor  should  be  governed  by  the  speed  of 
the  car.  In  this  way  the  truck  can  attain  its  maximum  speed  at 


SPEED-CONTEOLLING  DEVICES 


87 


a  moderate  engine  speed,  and  with  only  a  partly  opened  throttle. 
It  also  permits  the  motor  to  operate  at  a  higher  speed  on  the 
lower  car  speeds.  In  practice  with  the  proper  size  motor  for  a 
certain  car  capacity,  the  gear  ratio  is  generally  such  that  the 
maximum  safe  motor  speed  is  reached  in  second  speed,  so  that  the 
maximum  power  may  be  obtained  when  it  is  most  necessary.  The 
motor  should  not  be  permitted  to  develop  its  full  power  in  high 
gear,  as  gear  changes  are  provided  to  obtain  increasing  torque 
with  decreasing  car  speed.  Limiting  the  motor  power  in  high 
speed  is  an  advantage  up  to  a  certain  point,  for  a  truck  should 
never  be  permitted  to  take  a  hill  on  high  gear  if  it  is  necessary  to 
retard  the  spark  all  the  way. 


MECHANISM 


SECTION  of  GOVERNOR 
GEARS 


FIG.  62.     Centrifugal  Type  of  Governor. 

There  is  also  a  governor  on  the  market  at  the  present  time 
which  controls  both  the  motor  speed  and  the  car  speed,  the 
object  of  this  device  being  to  obtain  a  better  fuel  economy  and 
to  form  an  assistance  to  the  driver  in  operating  the  vehicle. 

While  still  another  automatic  governor  in  addition  to  con- 
trolling the  speed  also  operates  the  throttle  and  spark  and  con- 


88      MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

trols  the  motor  under  all  speeds.  The  operator  merely  sets  the 
governor  as  to  the  speed  he  wishes  to  make  and  the  governor  does 
the  rest. 

The  writer  is  attempting  to  cover  this  subject  in  such  a  way 
as  to  present  all  types  of  governors  now  in  use  and  those  which 
may  come  into  general  use. 

The  Centrifugal  Type. — Fig.  62  illustrates  a  centrifugal  type 
of  governor  which  has  been  used  by  a  number  of  prominent  com- 


WATER 
CHAMBER 


FIG.  63.     Hydraulic  Type  of  Governor. 

mercial  car  builders.  The  governor  is  placed  at  the  front  end  of 
the  motor  and  is  driven  through  spiral  gears  from  the  magneto 
drive  shaft.  As  the  motor  speed  increases  the  weighted  levers 
open  and  raise  a  sleeve  which  operates  the  auxiliary  throttle 
valve  in  the  intake  manifolds,  by  means  of  a  forked  lever  bearing 
in  the  sleeve  and  a  flexible  shaft  which  operates  a  rack  meshing 
with  a  small  gear  on  the  auxiliary  valve  shaft.  As  the  speed  de- 


SPEED-CONTROLLING  DEVICES 


89 


creases  the  pressure  of  the  governor  spring  returns  the  operating 
parts  to  their  neutral  position. 

The  Hydraulic  Type. — Fig.  63  shows  a  hydraulic  type  of  gov- 
ernor used  by  some  commercial  car  builders.  It  is  mounted  be- 
tween the  intake  manifold  and  the  carburetor.  The  operating 
mechanism  is  combined  in  a  unit  with  the  governor  proper,  mak- 
ing it  a  simple  -and  compact  unit.  The  water  chamber  is  con- 
nected with  the  water  pump  and  as  the  latter's  speed  increases, 
the  water  pressure  raises  and  forces  the  diaphragm  down.  This 
diaphragm  has  a  stem  which  bears  on  the  throttle  lever  and  is 
controlled  by  a  coiled  wire  spring.  The  lever  in  turn  forms  a 
segment  with  several  teeth  and  meshes  with  a  small  gear  on  the 
throttle  valve  shaft.  As  the  pressure  decreases  the  spring  re- 
turns the  diaphragm  to  its  original  setting  and  opens  the  throttle 
valve.  The  water  chamber  cover,  operating  lever  housing  and 
the  spring  retaining  plug  are  sealed  so  that  the  governor  cannot 
be  tampered  with,  without  first  breaking  either  one  of  the  three 
seals. 

In  both  of  the  above  types  the  maximum  speed  may  be 
changed  by  increasing  or  decreasing  the  spring  tension. 

The  Automatic  Type. — An  automatic  type  of  governor  is 
shown  in  Fig.  64,  in  which  the  speed  is  regulated  by  governing 

DISC 


SPRING 

CONTROLLi 

THSDISC 


FIG.  64.     Automatic-Type  GoverDor. 

the  velocity  of  the  inflowing  gases.  This  device  consists  of  a 
throttle  connected  to  a  disc  that  is  allowed  to  float  under  a  con- 
stant spring  tension,  in  a  tapered  conduit,  the  tension  of  the 
spring  determining  the  maximum  engine  speed.  The  slightest 
change  in  the  velocity  of  the  incoming  gases  caused  by  a  dif- 


90   MOTOE  TKUCK  DESIGN  AND  CONSTRUCTION 

ference  in  engine  speed  will  affect  the  position  of  the  disc  in  the 
conduit  and  also  change  the  position  of  the  throttle  immediately, 
giving  the  engine  more  or  less  gas  as  the  conditions  may  require. 
An  auxiliary  control  lever  is  provided,  giving  the  operator  access 
to  any  engine  speed  under  the  maximum  controlled  by  the  gov- 
ernor. This  governor  is  designed  to  be  mounted  between  the 
intake  manifold  and  the  carburetor  and  does  not  require  any 
form  of  drive  whatever,  its  operating  mechanism  being  self- 
controlled. 

The  Krebs  truck  is  equipped  with  a  centrifugal  type  of  gov- 
ernor which  controls  the  motor  and  car  speed.  The  spark  and 
throttle  are  so  connected  to  the  governor  that  it  constantly  sets 
them  for  the  power,  load  and  speed  that  may  be  required,  without 


FIG.  65.     Another  Type  of  Centrifugal    Governor. 

regard  to  road  conditions.  The  governor  is  also  so  contrived  that 
when  the  clutch  is  disengaged,  the  motor  continues  to  run  at  the 
same  speed,  preventing  the  driver  from  racing  the  engine.  En- 
gaging the  clutch  causes  the  throttle  to  open  wide  until  the  car 
reaches  the  speed  at  which  the  governor  is  set.  The  manufacturer 
of  this  governor  claims  that  it  takes  the  entire  responsibility  of 
handling  the  motor  at  all  speeds  and  all  loads.  This  governor  is 
shown  in  Fig.  65. 

Fig.  66  illustrates  the  Pierce  engine  governor,  which  also 
operates  on  the  centrifugal  principle.  It  differs  from  the  above 
in  that  it  is  designed  to  be  mounted  between  the  intake  manifold 


SPEED-CONTEOLLING  DEVICES 


91 


and  the  carburetor,  making  it  more  adaptable  to  motors  in  gen- 
eral. The  drive  may  either  be  taken  from  the  cam  shaft  of  the 
motor  or  countershaft  of  the  transmission.  As  the  motor  speed 


FIG.  66.     Pierce  Centrifugal  Type  Governor  and  Drive. 

reaches  the  maximum  setting  of  the  governor,  the  triangular 
weights  open  and  move  endwise  on  the  shaft  upon  which  they 
are  mounted,  which  in  turn  moves  the  operating  rod.  The  end 
of  this  rod  carries  a  rack  gear  which  is  in  mesh  with  a  small  gear 
on  the  butterfly  valve  shaft.  As  the  weights  close  a  spring  re- 
turns the  rod  to  its  neutral  position.  The  governor  also  has  a 
speed  adjustment,  so  that  any  desired  motor  speed  may  be  ob- 
tained. This  adjustment  is  sealed  so  that  it  cannot  be  tampered 
with. 

Fig.  67  shows  the  Pierce  speed  controller  which  operates  on 
the  same  principles  as  the  Pierce  governor.  The  drive  is  taken 
from  the  front  wheel  and  is  similar  to  a  speedometer  drive.  It 
is  so  constructed  that  it  is  impossible  to  remove  the  driving  gear 
without  breaking  the  seals  and  removing  the  front  wheel.  The 
triangular  weights  are  placed  at  right  angles  to  the  valve  op- 
erating rod,  the  governor  shaft  movement  being  transmitted 
through  a  bell  crank.  The  controller  is  provided  with  a  variable 
speed  dial,  which  changes  'the  spring  pressure  on  the  operating 
rod  and  permits f instant  adjustment  of  speed  to  suit  individual 
requirements,  automatically  controlling  vehicle  speed,  leaving  the 
motor  free  at  all  times.  This  controller  may  also  be  provided 
with  a  lock  so  that  it  is  impossible  for  any  one  to  start  the  vehicle 
without  the  key. 

The  housing  of  both  devices  are  made  of  aluminum,  so  that  a 
minimum  weight  is  carried  by  the  intake  manifold.  The  chief 
advantage  claimed  for  these  devices,  is  their  adaptability  to  any 
vehicle,  as  it  is  only  necessary  to  drop  the  carburetor  one  inch  to 
one  and  one-half  inches.  In  case  of  repairs  it  is  a  very  simple 


92      MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

matter  to  remove  the  governor  or  controller  entirely,  raise  the 
carburetor  and  the  vehicle  need  not  be  laid  up  pending  the  return 
of  either  device. 


THROTTLE  VALVE- 


RECULAT/NG 

D/XL 


FIG.  67.     Pierce   Centrifugal   Governor. 

The  Duplex  governor  shown  in  Fig.  68  was  designed  on  the 
principle  of  a  dual  actuating  influence.  This  dual  influence  con- 
sists of  a  motor  influence,  as  to  its  speed,  which  is  imparted  to  the 
governor,  and  a  vehicle  influence  which  is  also  imparted  to  the 
governor.  The  motor  speed  is  conveyed  from  some  revolving 
part  of  the  motor  to  one  of  the  speed  terminals  of  the  governor, 
and  the  vehicle  speed  from  the  propeller  shaft  or  jack  shaft.  The 
conveying  means  consists  of  a  steel  cable  revolving  in  a  hard  fiber 
or  metallic  casing.  The  governor  is  so  constructed  that  it  may  be 
mounted  between  the  intake  manifold  and  the  carburetor.  In- 


SPEED-CONTKOLLING  DEVICES 


93 


stead  of  the  ordinary  butterfly  valve  a  grid  valve  is  used,  through 
which  the  entire  gas  supply  must  pass.  This  grid  valve  consists 
of  a  fixed  part  set  into  the  upper  part  of  the  valve  chamber, 
which  is  provided  with  a  series  of  elongated  slots,  with  flaring 
walls  from  its  upper  surface  downward.  When  the  openings  of 


FIG.  68.     The  Duplex  Governor. 

both  fixed  and  movable  parts  coincide,  the  valve  is  open  and  when 
the  bars  of  one  part  cover  the  openings  of  the  other  part,  the 
valve  is  closed.  The  movable  part  is  held  open  by  spring  tension 
and  its  possible  motion  in  either  direction  is  limited  by  adjusting 
screws. 

Within  the  governor  there  are  two  automatically  acting  one- 
way clutches,  the  floating  members  of  which  consist  of  gears  in 
mesh  with  a  third  gear  mounted  on  the  centrifugal  governor 
spindle.  These  clutches  are  so  designed  as  to  impart  to  the  cen- 
trifugal member  that  of  the  two  speeds  which  is  the  higher.  With 
the  motor  running  idle,  the  motor  speed  will  actuate  the  governor, 
and  the  motor  is  always  under  governor  control.  When  the 
vehicle  is  propelled  by  the  motor  on  the  higher  gears,  the  speed 
imparted  to  the  governor  by  the  vehicle  will  be  the  higher  speed 
and  will  govern  the  motor, -whereas  on  the  low  gears  the  motor 
speed  will  be  the  higher  and  will  govern  the  motor. 

The  influence  of  the  centrifugal  member,  as  a  result  of  the 
speeds  imparted  to  it,  is  to  develop  a  pressure  sufficient  to  over- 
come the  spring  pressure  tending  to  hold  the  valve  open,  and  to 
close  it.  As  soon  as  the  pressure  is  removed,  the  movable  valve 
part  is  released  and  returned  to  its  full  open  position.  Provision 


94      MOTOK  TEUCK  DESIGN  AND  CONSTRUCTION 

is  made  for  adjustment,  which  is  enclosed  and  provided  with  a 
lock  so  that  it  cannot  be  tampered  with. 

These  various  types  of  governors  have  their  advantages  and 
disadvantages,  while  there  may  also  be  certain  disadvantages  to 
their  omission.  When  commercial  vehicles  are  not  equipped  with 
governors,  the  owner  is  forced  to  rely  entirely  upon  the  discretion 
of  the  operator,  while  the  manufacturer  must  rely  on  careful 
management  of  them  by  the  owners  to  prevent  the  evils  of  motor 
racing  and  excessive  speed.  This  also  applies  on  hills  where  it  is 
asserted  that  governors  are  of  no  use  in  preventing  excessive 
vehicle  speeds. 

There  are  some  who  claim  that  there  is  no  adequate  method 
yet  devised  which  is  capable  of  governing  a  truck  or  its  engine, 
without  handicapping  the  driver  somewhat  in  the  operation  of 
the  vehicle.  However,  the  writer  opines  that  it  is  worth  while 
fool-proofing  the  commercial  car  even  in  a  crude  way,  particu- 
larly in  speed.  With  solid  tires  and  the  tendency  to  overload 
commercial  vehicles,  the  speed  becomes  a  large  factor  in  obtain- 
ing long  life. 

It  may  be  said  that  certain  governing  devices  do  limit  the 
power  of  the  motor  on  the  lower  car  speeds.  However,  this  may 
not  be  as  serious  as  some  think,  as  these  vehicles  are  operated  on 
the  higher  speed  the  greater  portion  of  the  time. 

Some  also  claim  that  the  intelligence  and  general  ability  of 
the  commercial  vehicle  operator  exceeds  that  of  the  touring  car 
operator,  but  as  the  conditions  of  both  are  vastly  different,  it  is  a 
difficult  matter  to  determine  this  fact.  Truck  drivers  as  a  rule 
are  paid  a  certain  wage  for  a  stipulated  number  of  hours  per 
week,  and  if  they  are  delayed  long  enough  in  their  daily  trips 
to  make  their  work  exceed  this  stipulated  time,  they  will  try  and 
make  up  this  discrepancy  by  speeding  up  the  vehicle  whether 
loaded  or  empty. 

However,  it  should  be  remembered  that  there  is  a  certain  class 
of  conservative  operators  who  can  operate  a  vehicle  safely  with- 
out limiting  its  speed,  but  as  operators  of  this  class  are  few,  some 
means  must  be  resorted  to  for  limiting  the  destruction  of  trucks 
through  excessive  speeding. 

Many  manufacturers  equip  their  vehicles  with  governors  ad- 
mitting their  shortcomings,  arguing  that  even  though  the  econ- 
omy and  efficiency  of  the  truck  may  be  slightly  affected,  this  loss 
is  more  than  made  up  for  by  the  saving  in  depreciation  resulting 
from  the  unskilful  operation  of  careless  drivers. 


CHAPTER  VII 

THE  CLUTCH  AND  TRANSMISSION 

THE  defects  in  the  gasoline  engine,  relative  to  its  flexibility, 
have  been  previously  mentioned.  Among  these  is  the  inability 
of  the  motor  to  develop  its  full  torque  from  a  standstill.  The 
crank  shaft  of  the  motor  must  rotate  at  a  speed  consistent  with 
power  requirements,  while  the  road  wheels  must  rotate  consistent 
with  road  conditions,  or  as  the  operator  wills.  For  this  reason  it 
becomes  necessary  to  use  a  transmission.  The  motor  must  be 
started  by  a  hand  crank,  or  some  starting  device,  which  only  pro- 
duces enough  torque  to  just  turn  the  motor  over  against  compres- 
sion, so  that  it  becomes  necessary  to  disconnect  the  motor  from 
the  other  driving  units  of  the  vehicle  for  starting  and  after  the 
motor  has  attained  its  speed  to  connect  it  with  the  vehicle  again. 

For  this  purpose  a  device  must  be  used,  which  will  allow  a 
certain  amount  of  slippage  until  the  motor  speed  has  been  re- 
duced and  the  vehicle  speed  gradually  accelerated  to  such  a  point 
that  the  two  correspond,  in  this  way  preventing  shock  and  jar  to 
the  driving  mechanism. 

This  feature  is  accomplished  by  the  clutch,  which  is  most  gen- 
erally placed  in  close  proximity  to  the  motor.  The  most  popular 
position  is  inside  the  flywheel.  In  commercial  cars  a  single  clutch 
is  generally  employed,  which  serves  to  connect  the  engine  to  the 
driving  wheels  through  all  of  the  different  gear  reductions.  It  is 
normally  held  in  engagement  by  a  single  spring  of  large  diam- 
eter, or  by  a  number  of  smaller  springs,  and  is  controlled  by  a 
foot  pedal  to  disconnect  it  from  the  motor  by  releasing  the  fric- 
tion surfaces,  thus  disconnecting  the  power  of  the  motor  from 
the  driving  units.  When  it  is  desired  to  disconnect  the  engine  in 
order  to  stop  the  car,  or  to  change  the  gear,  the  clutch  is  first  dis- 
engaged by  foot  pressure  upon  the  pedal,  which  compresses  the 
spring;  the  gear  is  then  disengaged  or  changed  and  the  clutch 
let  in  again. 

There  are  quite  a  number  of  different  types  of  clutches,  all 
more  or  less  extensively  used,  as  follows :  Conical  clutches  of  the 
indirect  or  direct  type,  multiple  disc  clutches,  dry  plate  clutches, 
band  clutches,  and  combinations  of  cone  and  disc  type.  The 

95 


96      MOTOK  TKUCK  DESIGN  AND  CONSTRUCTION 

construction  of  each  type  varies  considerably  in  details  of  design 
and  the  materials  used  for  the  frictional  surfaces. 

In  light  commercial  cars  of  4,000-lbs.  capacity,  or  under, 
there  is  a  tendency  to  use  the  unit  power  plant,  in  which  the 
motor,  clutch  and  transmission  are  always  held  in  alignment, 
while  on  the  heavier  types  the  transmission  and  jack  shaft  are 
combined  in  a  unit  or  mounted  amidships  for  shaft  drive.  With 
the  latter  types  it  is  necessary  to  use  a  double  universal  joint  be- 
tween the  clutch  and  transmission  units.  The  universals  take  up 
any  misalignment  due  to  frame  weaving.  In  some  cases  they  are 
bolted  to  the  clutch,  spider  or  spigot,  while  in  others  they  are 
built  into  the  clutch  center.  This  latter  construction  seems  to  be 
gaining  favor  with  multiple  disc  clutches  which  operate  in  oil, 
a  portion  of  which  is  distributed  to  the  universal,  causing  it  to  be 
self-maintaining. 

A  variety  of  methods  are  resorted  to  for  mounting  the  clutch 
on  the  spigot,  plain,  ball  and  roller  bearings  being  used  for  this 
purpose. 

There  is  also  a  tendency  to  provide  clutch  brakes  so  that  the 
tendency  of  spinning  caused  by  the  inertia  may  be  reduced  to 
facilitate  gear  shifting. 

Cone  Types. — Among  the  conical  clutches  we  find  two  types 
in  general  use,  direct  and  indirect  types.  Either  type  consists  of 
a  male  and  female  member,  the  male  member  being  forced  into 
the  female  member  by  the  pressure  of  the  spring  or  springs. 
When  one  spring  is  used,  it  is  attached  to  the  clutch  spigot  and 
when  a  number  of  small  springs  are  used  they  are  attached  to  a 
spider,  which  is  free  to  float  on  the  clutch  spigot.  The  action  of 
the  clutch  members  is  similar  to  a  wedge  movement.  It  is  the 
oldest  type  and  also  the  simplest  type  in  use  at  present.  The  fly- 
wheel generally  forms  the  female  member  for  the  direct  type, 
while  the  male  member  may  either  be  made  from  aluminum  or 
pressed  steel  and  covered  with  a  material  such  as  Raybestos, 
leather,  etc.  In  the  indirect  type  it  is  necessary  to  bolt  the  female 
member  to  the  flywheel.  The  clutch  spigot  may  either  be  an  ex- 
tension of  the  crank  shaft  or  it  may  be  bolted  to  the  flywheel. 

Fig.  69  serves  to  illustrate  the  general  construction  of  the 
direct  type.  The  male  member  is  provided  with  cork  inserts  to 
obtain  a  higher  coefficiency  of  friction  and  is  bolted  to  a  cast- 
steel  housing,  which  is  mounted  on  the  clutch  spigot  and  sur- 
rounds the  clutch  spring.  The  spigot  is  formed  by  an  extension 
of  the  crank  shaft,  and  is  provided  with  a  thrust  bearing. 


THE  CLUTCH  AND  TRANSMISSION 


97 


The  cone  clutch,  depicted  in  Fig.  70,  differs  from  the  above  in 
that  three  small  springs  are  used.  These  small  springs  are  sup- 
ported on  studs,  which  are  riveted  to  the  clutch  spider.  The 
spider  is  provided  with  a  die-cast  babbitt  bearing  instead  of  a 


PRESSED 

STEEL 

CONE 


SPRING  A  NO 
-PLUNGER 


FIG.  69.     General  Construction  of  Direct      FIG.  70.      Cone    Clutch    with 
Cone.  Three    Small   Springs. 

cast-bronze  bearing.  It  depicts  a  type  which  is  generally  incor- 
porated in  the  unit  power  plant,  owing  to  its  short  length,  .which 
is  a  desirable  feature. 

An  indirect  type  of  cone  clutch  is  shown  in  Fig.  71.  The  male 
member  is  made  of  aluminum  and  is  provided  with  a  fractional 
lining  and  cork  inserts.  Small  pieces  of  rubber  are  placed  under 
the  lining  to  obtain  a  smooth  and  gradual  engagement.  The 
female  member  is  made  of  gray  iron  arid  bolted  to  the  flywheel. 
It  also  forms  the  retaining  member. 

The  spigot  is  bolted  to  the  flywheel  and  provided  with  a 

bronze  bearing,  while  a  roller  bearing  is  used  as  a  thrust  bearing, 

and  the  disengaging  collar  is  provided  with  a  ball-thrust  bearing. 

Cone  clutches  of  both  types  are  also  provided  with  flat  springs,  or 

8 


98      MOTOE  TEUCK  DESIGN  AND  CONSTEUCTION 


plungers,  and  coil  springs,  which  are  placed  under  the  fractional 
facing,  the  object  being  to  prevent  the  tendency  to  jerk  when  first 

engaged.  The  friction  ma- 
terial is,  in  most  cases,  riv- 
eted to  the  male  member, 
while  in  a  few  cases  T-head 
bolts  are  used  to  facilitate  its 
replacement,  while  one  or  two 
makers  rivet  it  to  the  female 
member. 

Multiple-disc  Type.— Multi- 
ple disc  and  plate  clutches  are 
based  on  the  same  principle  as 
the  cone  clutch,  but  constitute 
in  a  sense  extreme  opposites  in 
design.  This  type  offers  sev- 
eral advantages  not  found  in 
the  others,  being  the  most  com- 
pact. The  required  frictional 
surface  is  obtained  by  a  mul- 
tiplicity of  small  surfaces,  in 
preference  to  two  large  ones, 
as  in  the  case  of  the  cone  and 
plate  types. 

A  disc  clutch  consists  of  two  sets  of  discs,  one  set  being  termed 
the  driving  discs  and  the  other  the  driven  discs.  The  driving 
discs  are  generally  provided  with  key  slots  on  their  outer  circum- 
ference, which  fit  over  hardened  steel  keys  riveted  to  the  inside 
circumference  of  the  housing  bolted  to  the  flywheel.  The  driven 
discs  are  also  provided  with  key  slots,  but  these  are  placed  on 
their  inner  circumference,  which  fit  over  keys  riveted  to  a  hous- 
ing attached  to  the  driven  shaft.  It  is  general  practice  to  use  one 
more  driving  disc  than  there  are  driven  discs,  so  that  the  two  end 
discs  may  be  of  the  same  kind.  The  driving  set  is  driven  by  the 
engine,  while  the  remaining  set  is  attached  to  a  continuation  of 
the  transmission  shaft.  In  some  cases  small  flat  springs  are  used 
to  keep  the  discs  apart  under  conditions  where  it  is  desired  to 
render  the  clutch  inoperative,  that  is,  when  the  spring  pressure  is 
removed  from  them. 

It  is  usual  practice  to  enclose  a  clutch  of  this  kind  in  an  oil- 
tight  case,  which  insures  that  the  members  will  operate  in  a  con- 
stant bath  of  oil,  meaning  long  life  of  the  frictional  surface  as 


FIG.  71.     Indirect  Cone  Type. 


THE  CLUTCH  AND  TRANSMISSION 


99 


well  as  gradual  engagement.    Owing  to  its  comparatively  small 

diameter,  the  inertia  is  not  very  great  and  gear  shifting  is  some- 
what easier  than  with  the 

cone    clutch.      The    spring 

pressure  is  great  enough,  so 

that    when    engagement    is 

made  the  oil  will  be  squeezed 

from    between    the    plates 

and  the  frictional  surfaces 

brought   into   contact.     As 

the  oil  is  gradually  squeezed 

out,  and  as  there  will  be  a 

certain  amount  of  slippage 

as  long  as  any  considerable 

amount    of    lubricant    re-        FIG.  72.    Helle  Shaw.   Multiple-Disc 

mains,    the    power    will    be  Clutch.     Universal  Type. 

applied  gradually. 

A  multiple-disc  clutch,  which  is  ex- 
tensively used  in  commercial  cars  in 
this  country  and  abroad,  is  the  Hele- 
Shaw  clutch,  illustrated  in  Fig.  72. 
The  discs  are  niade  from  steel  and 
bronze,  with  V-groove  corrugations. 
Only  the  walls  of  these  grooves  come 
in  contact  and  the  remaining  portions 
of  the  disc  serve  to  radiate  the  heat  en- 
gendered during  slippage.  To  permit 
the  oil  to  enter  and  escape  freely,  these 
discs  have  small  holes  drilled  in  the 
inner  walls  of  the  grooves  near  the 
peak.  The  action  obtained  by  these 
grooves  is  a  wedge  action  similar  to  the 
cone  clutch.  This  also  illustrates  a  de- 
sign in  which  pressed  steel  is  used 
wherever  it  is  possible  to  do  so.  The 
clutch  is  of  the  universal  type,  having 
an  external  and  internal  gear  type  of 

universal,  mounted  inside  of  the  clutch.    A  clutch  brake  is  also 

provided  to  facilitate  gear  shifting,  this  brake  being  mounted 

upon  the  drive  shaft  and  adjustable  for  wear. 

Fig.  73  is  a  type  of  multiple-disc  clutch  used  in  connection 

with  unit  power  plants.     It  is  built  onto  an  extension  of  the 


FIG.  73.  Type  of  Mul- 
tiple-Disc Clutch  used  in 
Unit  Power-Plants. 


100    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

transmission  shaft,  one  end  of  which  is  supported  by  a  ball  bear- 
ing in  the  flywheel.  The  frictional  surfaces  consist  of  saw-steel 
driving  discs  and  Raybestos-line,  steel-driven  discs.  The  con- 
struction is  similar  to  those  described  above,  excepting  that  two 
large  springs  are  used,  one  being  placed  around  the  other  and 
retained  by  three  bolts,  which  provide  adjustment  for  the  spring 
tension. 

The  housing  or  driving  member  bolted  to  the  flywheel  has 
teeth  cut  on  its  inner  periphery  into  which  the  plates  fit  instead 
of  keys  and  the  plates  have  teeth  instead  of  key  slots. 

Dry-plate  Type. — The  dry-plate  clutch  is  similar  to  the  mul- 
tiple-disc type ;  however,  the  discs  are  of  a  much  larger  diameter 


FIG.  74.     Bore  &  Beck  Dry  Plate  Clutch. 

and  but  three  or  five  plates  are  necessary.    The  driving  discs  are 
either  Raybestos  rings  or  bronze  plates  with  cork  inserts,  while 


THE  CLUTCH  AND 


the  driven  discs  are  made  of  steel.  These  clutches  are  not  de- 
signed to  run  in  oil,  but  are  liable  to  wear  because  of  the  amount 
of  contact  surface  provided. 

A  popular  three-plate  clutch  of  conventional  design  is  shown 
in  Fig.  74.  The  face  of  the  flywheel  forms  one  surface,  while  a 
moving  member  forms  the  other.  Between  them  are  two  discs 
of  friction  material  and  a  floating  member  which  is  keyed  to  the 
driving  shaft.  Pressure  is  obtained  by  coiled  spring  acting  on  a 
sleeve  which  actuates  the  toggle  mechanism  operating  the  mov- 
able member.  This  toggle  mechanism  is  supported  by  a  disc 
which  is  bolted  to  the  flange.  This  flange  has  two  slots  through 
which  the  bolts  pass  and  this  together  with  taper  surfaces  on  the 
movable  member  form  a  means  adjustment  for  wear  of  the  fric- 
tion discs. 

In  Fig.  81  is  shown  a  simple  plate  clutch  for  low  power  de- 
livery cars.  This  clutch  is  almost  entirely  of  pressed  steel  and 
utilized  the  flywheel  as  a  driving  member.  Two  additional  driv- 
ing plates  are  used  and  these  are  supported  by  three  hardened 
steel  pins  fastened  to  the  flywheel,  which  also  carry  the  springs. 
The  driven  member  consists  of  a  spur  gear  which  supports  the 
driven  plates  that  have  teeth  cut  on  their  inner  periphery. 


FIG.  75.     Hilliard  Clutch  with  Double  Annular  Ball  Bearing  and  Enclosed 

Spring. 

The  Hilliard  clutch   (Fig.  75)   is  another  excellent  example 
of  the  plate  type.    Spinning  of  the  rotating  members  is  prevented 


102    MOfrDB^  TRtJ€K  DESIGN  AND  CONSTRUCTION 


by  a  combination  of  quick  acting  release,  which  does  not  permit 
of  a  drag  while  releasing  and  further  by  having  the  parts  so  light 
that  rotation  does  not  continue  long. 

Band  Type.  —  Band  clutches  are  practically  the  same  in  gen- 
eral principle  of  operation,  as  band  brakes,  and  are  of  the  same 
general  types,  internal  expanding  and  external  contracting.  This 
type  of  clutch  is  not  very  popular,  and  but  few  can  be  found  on 
commercial  cars  at  present. 

There  is  a  tendency  on  the  part  of  manufacturers  to  use  ball 
bearings  for  supporting  clutches  of  all  types,  as  the  plain  bearing 
is  hard  to  lubricate  effectively  and  the  friction  of  same  tends  to 
produce  dragging.  The  ball  bearing  can  be  more  easily  lubri- 
cated, requires  less  attention  and  eliminates  this  dragging  evil. 

Comparisons.  —  The  advantages  of  the  cone  clutch  are  that  it 
may  be  engaged  and  disengaged  with  very  small  axial  motion, 
axial  pressure  may  be  low  because  the  normal  pressure  between 
f  rictional  surfaces  is  multiplied  by  the  angularity  of  the  cone,  its 
weight  is  not  very  great  as  the  male  member  may  be  made  of 
aluminum  or  pressed  steel,  its  engagement  is  entirely  independent 
of  speed  and  centrifugal  force,  no  liquid  lubricant  is  needed  with 
attending  viscosity,  drag  and  change  due  to  wear  and  tem- 
perature. Disengagement  may,  therefore,  be  made  perfect.  The 
chief  disadvantage  of  this  clutch  is  its  size,  it  being  more  bulky 
than  the  other  types  with  the  possible  exception  of  the  dry-plate 
type.  Inertia  is  also  a  disadvantage,  as  this  must  be  as  small  as 
possible,  in  order  to  make  gear  shifting  easy  and  to  avoid  gear 
clattering. 

These  objections  led  to  the  introduction  of  the  multiple-disc 
clutch,  in  which  the  frictional  surface  can  be  made  larger  and  the 
f  rictional  force  smaller  per  unit  surface.  The  chief  disadvantage 
of  multiple-disc  clutch  is  its  tendency  to  drag  if  the  oil  in  the 
clutch  housing  is  not  suitable  for  the  purpose.  Most  makers 
recommend  a  light  machine  or  cylinder  oil  and  kerosene.  It  can 
readily  be  understood  that  the  thinner  the  lubricant,  the  better 
the  clutch  will  hold,  while  the  more  viscous  lubricant  will  permit 
it  to  pick  up  its  load  more  gradually. 

To  overcome  the  dragging  evil,  the  dry  disc  type  was  intro- 
duced. The  surfaces  are  not  lubricated  but  are  most  generally 
provided  with  frictional  facings  in  order  to  increase  the  co- 
efficient of  friction.  This  clutch  has  its  disadvantages  of  inertia, 
similar  to  the  cone  type. 


THE  CLUTCH  AND  TKANSMISSION  103 

The  combination  of  dry  plate  and  cone  has  the  features  of  the 
dry  plate,  its  tendency  to  gradually  pick  up  its  load  and  the  hold- 
ing power  of  the  cone  after  it  has  assumed  its  load.  It  is  also 
simple  in  construction.  However,  it  requires  frequent  adjustment. 

At  the  present  time,  the  cone,  multiple  disc  and  plate  clutches 
are  by  far  the  most  popular  and  seem  to  be  holding  their  own, 
with  all  the  new  types  which  are  being  experimented  with. 

The  Transmission. — In  every  gasoline  engine  it  is  absolutely 
necessary  that  some  method  be  used  for  changing  the  relation  be- 
tween the  speed  and  power  of  the  car.  When  a  gasoline  engine 
is  loaded  above  a  certain  limit  it  slows  down,  and  the  intervals 
between  the  explosion  in  each  cylinder  become  so  far  apart  as  to 
cause  the  engine  to  labor  and  finally  stop  altogether,  unless  some 
means  is  used  to  increase  the  speed  of  the  engine  by  decreasing 
the  load  upon  it.  In  considering  this  subject  it  must  be  remem- 
bered that,  when  a  car  is  using  its  maximum  power,  it  may  be 
divided  either  into  considerable  pulling  power  with  slow  speed, 
or  high  speed  with  low  pulling  power.  Consequently,  when  a  car 
is  going  at  high  speed  and  a  considerable  grade  or  a  stretch  of 
heavy  road  is  encountered,  the  car  will  begin  to  slow  down  until 
the  speed  reaches  such  a  point  that  the  engine  begins  to  knock 
and  labor.  When  this  point  is  reached,  it  becomes  necessary  to 
change  to  a  slower  gear,  which,  for  the  same  speed  of  the 
vehicle,  gives  a  considerably  greater  number  of  revolutions  of 
the  engine,  with  a  consequently  larger  pulling  power. 

This  pulling  power  is  termed  "  torque,"  and  if  gasoline  engines 
could  be  designed  as  to  afford  an  increasing  torque,  with  decreas- 
ing speed,  all  would  be  well  and  the  transmission  could  be  elim- 
inated. As  it  is  taking  into  account  the  power  of  the  motor  at 
several  speeds,  nothing  of  this  sort  can  be  considered.  At  very 
low  speed  torque  becomes  of  greatest  importance,  and  this  is  espe- 
cially true  in  vehicle  operation. 

The  use  of  the  transmission  is  also  necessary  in  starting  the 
vehicle,  because  until  the  vehicle  reaches  a  certain  momentum, 
there  is  considerable  load  on  the  engine,  so  that  a  slow  speed 
which  allows  a  high  number  of  revolutions  of  the  motor  must  be 
used. 

It  is  generally  understood  that  to  reverse  the  motion  of 
the  commercial  car  engine  is  to  labor  under  disadvantages  in 
numerous  ways.  Power  will  be  lost,  owing  to  the  inferior  valve 
timing  relation  which  must  follow  if  the  cam  shaft  was  designed 


104    MOTOE  TKUCK  DESIGN  AND  CONSTRUCTION 


to  suit  reversing  condition.  Unless  certain  complications  were 
introduced  in  the  valve  action,  and  since  in  any  case  it  would  be 
necessary  to  add  to  the  flexibility  of  the  motor  by  the  use  of  a 
transmission,  it  would  seem  unnecessary  to  add  to  the  valve 
motion  anything  by  the  way  of  complicated  devices.  An  addi- 
tion to  the  gear  set  is  less  complicated  and  the  end  is  adequately 
served. 

Types. — The  most  popular  transmissions  are  the  friction, 
planetary  and  sliding  gear.  The  friction  and  planetary,  with 
few  exceptions,  are  only  used  on  the  light  vehicles,  while  the  slid- 
ing gear  type  is  extensively  used  on  all  sizes  of  vehicles. 

Friction  Type. — There  are  two  types  of  friction  transmission 
in  use  at  the  present  writing,  the  single  disc  and  the  double  disc. 
This  single-disc  type  consists  of  a  driving  disc  which  is  attached 
to  the  flywheel  or  an  extension  of  the  crank  shaft,  and  always 
rotates  with  it  and  a  driven  disc  which  can  be  slid  along  a  cross 

shaft  and  brought  into 
f  rictional  engagement  with 
the  driving  disc.  By  mov- 
ing the  driven  disc  out 
from  the  center  of  the 
driving  disc  the  speed  can 
be  varied  from  nothing 
to  maximum,  and  by  slid- 
ing it  to  the  opposite  side 
the  direction  of  motion  is 
reversed.  Before  the 
wheel  is  slid  in  the  direc- 
tion of  its  axis  it  must  be 
disengaged  from  the  driv- 
ing disc.  This  is  accom- 
plished by  either  moving  the  cross  shaft  and  its  bearings  or  by 
moving  the  driven  disc.  From  this  cross  shaft  the  final  drive  may 
be  through  a  single  chain  to  the  rear  axle,  or  it  may  be  through 
a  single  chain  to  the  jack  shaft  and  then  through  double  side 
chains  to  the  road  wheels.  Fig.  76  illustrates  a  friction  trans- 
mission of  the  single-disc  type.  The  discs  are  shown  in  the  high 
position,  while  the  lower  speeds  are  obtained  by  moving  the 
driven  disc  in  towards  the  center,  and  reverse  is  obtained  by  mov- 
ing the  driven  disc  toward  the  opposite  side  of  center. 

Planetary  Type. — The  planetary  transmission  is  somewhat 
cheaper  to  manufacture  than  the  sliding  gear  type  and  also  re- 


FIG.  76. 


Single-Disc  Friction-Type 
Transmission. 


THE  CLUTCH  AND  TRANSMISSION 


105 


quires  less  skill  in  operation.  There  are  two  types  of  planetary 
gears,  those  comprising  internal  gears  and  those  comprising  only 
spur  gears  in  their  makeup.  The  latter  is  the  most  popular  type 
and  will  be  considered. 

Fig.  77  depicts  this  type  of  transmission,  and  its  principle  of 
operation  may  be  described  as  follows : 


FIG.  77.     Planetary  Transmission  with  Spur  Gears. 

The  driving  shaft  A  carries  the  driving  pinion  B,  which 
meshes  with  the  planetary  pinion  G.  The  latter  forms  part  of 
sets  of  three  pinions  which  are  formed  integral.  D  is  the  low- 
speed  planetary  pinion  meshing  with  the  low-speed  gear  E  which 
is  secured  to  the  driven  shaft  F.  By  applying  the  brake  band  G 
to  the  combined  pinion  carrier  and  drum  H,  the  planetary  pin- 
ions are  held  stationary  in  space  and  act  like  a  back  gear.  Pinion 
B  rotating  in  a  right-hand  direction  (see  end  diagram),  turns 
pinions  G  and  D  on  their  pin  M  in  a  left-hand  direction,  and 
pinion  D  turns  gear  E  and  the  driver  shaft  F  in  a  right-hand 
direction ;  that  is,  in  the  same  direction  as  the  driving  pinion  B. 

For  reverse,  band  7  is  applied  to  the  drum  /,  which  has  the 
reversing  pinion  K  keyed  to  it,  being  thus  held  stationary  when 
pinion  B  is  rotated  by  the  engine  planetary  pinion  Z,  is  forced  to 
roll  on  K  in  a  left-hand  direction,  carrying  the  pinion  pin  M  and 
pinion  driver  PI  with  it. 

Direct  drive  is  obtained  by  engaging  the  high-speed  clutch 


106    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

N)  which  locks  the  reversing  gear  K  to  the  driving  shaft  J.,  and 
since  two  equal  gear  B  and  K  are  now  secured  to  the  shaft  A^  the 
planetary  pinions  are  locked  against  axial  motion  and  the  whole 
transmission  revolves  as  a  unit. 

Sliding-gear  Type. — The  sliding-gear  type  of  transmission 
consists  of  two  parallel  shafts  mounted  on  suitable  bearings  in  a 
housing  called  the  transmission  case.  The  first  of  these  shafts  is 
known  as  the  primary  or  main  driving  shaft.  This  shaft  is 
divided  into  two  parts,  the  forward  or  driving  part  and  the  rear 
or  driven  part,  the  latter  being  provided  with  a  bearing  at  its  for- 
ward end,  inside  the  former.  The  second  of  these  shafts  is  known 
as  the  secondary  or  countershaft.  The  driven  part  of  the  main 
shaft  is  either  squared  or  provided  with  integral  keys  and  carries 
the  sliding  gears,  whose  common  hubs  have  squared  holes  or  key- 
ways  to  coincide  with  the  shaft  to  make  a  sliding  fit  upon  it.  The 
driving  part  of  the  main  shaft  is  provided  with  a  gear,  which 
meshes  with  a  gear  on  the  countershaft  and  forms  a  drive  for  the 
latter.  The  countershaft  has  a  number  of  gears  fixed  upon  it, 
depending  upon  the  number  of  speeds.  The  gears  on  both  shafts 
are  so  spaced  that  by  shifting  the  primary  set  corresponding 
gears  on  the  two  shafts  can  be  brought  into  mesh  successively 
without  interference  from  the  other  gears.  Shifting  of  the  slid- 
ing set  is  accomplished  by  means  of  a  hand  lever  located  con- 
veniently to  the  operator  and  a  suitable  connecting  linkage.  The 
shifter  rod  carries  a  fork,  which  is  attached  to  the  gears  in  such 
a  manner  as  to  permit  them  to  rotate  with  their  shaft. 

There  are  two  common  arrangements  of  shafts.  In  some 
cases  the  countershaft  is  located  below  the  main  shaft,  while  in 
others  the  two  shafts  are  located  in  a  horizontal  plane. 

When  the  shafts  are  placed  vertically  the  case  is  generally 
cast  in  one  piece,  with  a  large  hole  cover  plate  for  inspection  pur- 
poses. When  the  shafts  are  placed  in  a  horizontal  plane,  the  case 
may  either  be  cast  in  one  piece  or  in  halves  joined  through  the 
centers  of  the  bearings. 

There  are  three  general  methods  of  mounting  the  sliding  gear 
transmission:  combining  them  with  the  motor  to  form  a  unit 
power  plant,  individual  mounting  on  a  sub-frame  or  main  frame 
cross  members,  and  combining  them  in  a  unit  with  the  jack  shaft. 

All  of  these  mountings  may  be  made  with  a  more  or  less  de- 
gree of  flexibility.  Three-point  support  is  most  generally  re- 
sorted to,  with  the  intention  of  relieving  the  case  of  the  stresses 
set  up  by  frame  weaving. 


THE  CLUTCH  AND  TRANSMISSION 


107 


Progressive  Sliding  Type. 
— In  the  progressive  type 
of  transmission  all  sliding 
gears  are  moved  simulta- 
neously when  a  speed 
change  is  made.  The  sev- 
eral speeds  are  arranged  in 
a  fixed  succession  as  the 
combination  of  sliding 
gears  is  progressively 
shifted.  It  is  thus  neces- 
sary to  shift  into  the  low- 
speed  gear  first  and  progress 
to  the  high. 

Fig.  78  is  a  diagram- 
matic view  of  a  three-speed 
and  reverse  progressive 
transmission  which  is  used 
on  a  number  of  heavy  com- 
mercial cars. 

High  speed  is  obtained 
by  meshing  the  jaw  clutches 
formed  integral  with  the 
sliding  member  and  the 
constant  mesh  gear  F. 
Second  speed  is  obtained 
by  moving  the  sliding  mem- 
ber backward  and  mesh- 
ing gears  D  and  E,  so  that 
the  drive  is  through  gears 
F,  /,  E  and  D.  For  low 
speed  the  sliding  member  is 
moved  backward  so  that 
the  gear  B  will  mesh  with 
the  gear  C  on  the  counter- 
shaft, and  the  drive  is 
through  the  gears  F,  /,  C 
and  B.  For  reverse,  gear 
B  of  the  sliding  set  is 
meshed  with  the  reverse 
pinion  #,  which  is  con- 
stantly in  mesh  with  the 


U 

FIG.  78.  Diagram  of  Three-Speed 
and  Eeverse  Progressive  Sliding-Gear 
Transmission. 


108    MOTOE  TEUCK  DESIGN  AND  CONSTEUCTION 


gear  H  on  the  countershaft,  .and  the  drive  is  through  gear  F,  I, 
H,  G  and  B.  This  also  illustrates  a  unit  construction  of  jack 
shaft  and  transmission. 

Fig.  79  illustrates  the 
non-direct  type  of  change 
gear,  the  principle  of  op- 
eration being  similar  to  the 
above,  excepting  that  the 
high  speed  is  obtained  by 
meshing  gears  instead  of 
jaw  clutches,  while  the  up- 
per shaft  forms  the  drive 
and  carries  the  fixed  gears. 
The  lower  is  the  driving 
shaft  and  carries  the  slid- 
ing gears.  Since  the  high 
speed  is  obtained  by  mesh- 
ing gears,  the  drive  shaft 
may  be  constructed  in  one 
piece. 

The  principal  objection 
to  the  progressive  type  is 
that  it  requires  long  shafts, 
which  are  likely  to  be  in- 
efficiently rigid  and  to 
spring  and  bend  under  the 
thrust  of  the  gear  teeth, 
causing  noisy  and  inefficient 
operation.  The  great  length 
of  this  transmission  is 
mainly  due  to  the  fact  that 
that  the  gears  on  each  of 
the  shafts  must  be  spaced 
relatively  far  apart,  so  as  to 
avoid  interference. 


FIG.  79.     Non-Direct  Progressive  Type. 


Selective  Sliding  Type. 
—  This  objection  is  over- 
come  jn  the  selective  gliding 

type,    as    two    sliding    sets 

are  used.    By  comparing  the  two  types  it  will  be  noted  that  the 
latter  is  much  more  compact.    It  also  has  an  advantage  in  that 


THE  CLUTCH  AND  TRANSMISSION 


109 


the  operator  may  change  directly  from  one  speed  to  any  other 
without  passing  through  the  intervening  gears. 

Fig.  80  shows  a  three-speed 
forward  and  reverse  selective 
type  transmission.  The  primary 
shaft  is  squared  and  carries  two 
which 


sliding 


gears, 


are     op- 


erated by  independent  shifter 
rods.  The  countershaft  is  driven 
through  constant  mesh  gears  A 
and  B,  A  being  driven  by  the 
drive  shaft  extending  from  the 
clutch.  In  effecting  the  different 
speeds,  gear  C  is  moved  forward 
and  meshed  with  gear  D  for  low 
speed,  while  for  reverse  it  is 
moved  backward  and  meshed 
with  the  reverse  pinion  E,  which 
is  in  constant  mesh  with  the  re- 
verse gear  II  on  the  counter- 
shaft. For  second  speed  the  gear 
F  is  meshed  with  gear  (2,  while 
for  high  speed  gear  /,  which  is 
integral  with  gear  F,  is  moved 
for\vard  and  meshed  with  the  in- 
ternal gear  formed  integral  with 
the  constant  mesh  gear  A.  This 
forms  another  type  of  jaw  clutch, 
and  in  some  cases  the  jaw  clutch 
described  above  is  used  for  effect- 
ing the  high  speed. 

A  typical  unit  power-plant 
transmission  is  shown  in  Fig.  81. 
This  transmission  is  intended  for 
low-powered  delivery  cars  and 
is  provided  with  ball  bearings 
for  the  main  shaft  while  the  four 
counter-shaft  gears  are  cut  in 
one  and  are  provided  with  plain  bearings.  This  shows  the 
method  of  mounting  the  clutch  on  the  forward  main  shaft. 

Fig.  82  depicts  a  typical  four-speed  transmission  for  amidship 
mounting.    The  main  shaft  is  mounted  on  ball  and  roller  bear- 


FIG.  80.  Three  Speed  and  Re- 
verse Selective  Sliding  Transmis- 
sion. 


110    MOTOR  TEUCK  DESIGN  AND  CONSTRUCTION 


CHANGE  GEAR  V          a 


CLUTCH/]\        BRAKE 
PEDAL       II        PFDAL 


FIG.  81.     Conventional  Type  of  Unit  Power  Plant  Transmission  and  Con- 
trol Mounting. 


FIG.  82.     Four  Speed  Selective  Sliding  Gear  Transmission  for  Amidship 

Mounting. 


THE  CLUTCH  AND  TEANSMISSION 


111 


ings,  while  the  countershaft  is  mounted  on  roller  bearings.  The 
shifter  rods  are  mounted  in  the  cover  and  are  provided  with  locks 
for  the  various  speeds.  High  speed  is  obtained  by  meshing  two 
jaw  clutches  this  is  the  direct  drive,  third  by  meshing  gears  A 
and  B,  second  by  gears  G  and  D  and  low  speed  through  gears  E 
and  F.  For  reverse  speed  two  idler  gears  G  and  H  are  used, 
which  are  so  arranged  that  they  may  be  moved  along  their  shaft 
and  meshed  with  gears  E  and  F,  the  latter  being  held  in  its 
neutral  position. 


FIG.  83.     Constant  Mesh  Type  of  Selective-Sliding  Gear  Transmission. 

The  positive  clutch  type  of  transmission  is  somewhat  related 
to  the  selective  sliding  gear  type.  However,  the  gears  remain 
constantly  in  mesh,  and  the  gears  on  the  main  shaft  are  normally 
free  to  turn  thereon,  but  may  be  fixed  to  the  shaft  by  positive 
clutches.  These  clutches,  when  of  the  jaw  type,  are  similar  to 
those  mentioned  above,  while  internal  and  external  gears  may 
also  be  used  as  positive  clutches.  The  gears  on  the  main  shaft  are 
fixed  while  the  clutches  are  free  to  slide  upon  keys  or  squared 
portions  of  the  shaft. 

In  this  type  the  speed  changes  are  obtained  by  the  individual 
clutches,  but  since  the  high  speed  is  direct  through  the  case  and 
the  speed  of  the  countershaft  is  reduced  through  the  constant 
mesh  gears,  a  provision  must  be  made  so  that  the  latter  shaft 


112    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


THE  CLUTCH  AND  TRANSMISSION  113 

cannot  turn  on  its  bearings.  This  is  accomplished  by  disengag- 
ing a  clutch  on  the  countershaft,  simultaneously  with  the  engage- 
ment of  the  high-speed  clutch.  Fig.  83  illustrates  this  type  of 
transmission.  It  also  presents  a  method  of  driving  all  four 
wheels  by  the  addition  of  another  shaft  and  silent  chain. 

An  Automatic  Engagement  Type. — Fig.  84  illustrates  the  type 
of  jaw-clutch  transmission  used  on  the  Vulcan  trucks.  The 
clutches  are  shifted  automatically  and  are  slightly  undercut  so 
that  they  will  not  release  until  the  driving  pressure  is  removed, 
while  the  change  from  one  speed  to  another  is  made  by  means  of 
springs.  This  action  is  accomplished  as  follows:  moving  the 
gear-shift  lever  compresses  a  set  of  springs  which  control  the 
arms  which  move  the  jaw  clutches.  However,  as  the  clutches  are 
undercut  this  spring  action  has  no  effect,  but  just  as  soon  as  the 
engine  speed  is  momentarily  reduced  there  is  a  tendency  for  the 
vehicle  to  drive  the  engine,  which  instantly  frees  the  jaw  clutch, 
which,  under  the  action  of  the  compressed  springs  already  set  by 
the  movement  of  the  gear-shift  lever,  forces  the  clutch  to  take  up 
its  new  position,  engaging  the  desired  speed.  This  means  that 
slightly  throttling  the  engine  and  releasing  the  clutch  will 'always 
effect  the  desired  change  of  gears,  but  this  may  not  take  place 
until  any  desired  moment  after  the  gear-shift  lever  -has  been 
moved.  By  this  arrangement  it  is  possible  for  the  driver  to  ap- 
proach a  hill  and  before  reaching  it,  if  he  thinks  it  too  steep  for 
the  highest  speed,  he  can  set  the  lever  for  the  next  speed.  The, 
jaw  clutch  will  not  shift  as  long  as  the  engine  is  driving  until  at 
the  desired  moment  on  the  hill,  by  releasing  the  clutch  the  .change 
will  be  automatically  effected. 

Transmission  gears  are  usually  lubricated  by  a  non-fluid  oil. 
For  easy  introduction  of  the  lubricant,  a  hole  is  provided  in  the 
cover  plate,  which  is  enclosed  by  a  screw  plug,  while  a  drain  plug 
is  usually  placed  at  the  bottom  so  that  the  stale  lubricant  may  be 
washed  out  with  kerosene  or  gasoline.  The  bearing  caps  are  in- 
variably provided  with  felt  washers,  while  all  other  parts  are  pro- 
vided with  paper  gaskets,  to  prevent  the  lubricant  from  working 
out  of  the  case. 


CHAPTER  VIII 


UNIVERSAL  JOINT  AND  PROPELLER   SHAFT 

THERE  is  a  difficulty  in  transmitting  the  power  of  the  motor 
to  the  transmission  or  rear  axle  which  has  to  be  met  by  a  special 
piece  of  mechanism.  In  the  chain-driven  vehicle  the  motor  and 
transmission  usually  remain  in  alignment  when  the  vehicle  is 
standing  still,  however,  road  vibrations  and  the  nature  and  loca- 
tion of  the  load  usually  cause  frame  deflexions  which  tend  to  de- 
stroy this  alignment,  while  with  a  live  rear  axle  the  motor  is  pro- 
tected from  bouncing  up  and  down  by  the  chassis  springs,  and 
the  road  wheels  are  continually  bouncing  over  the  rough  surface 
of  the  road.  This  means  that  at  one  moment  the  axle  is  in  line 
with  the  motor  and  the  next  moment  it  may  be  several  inches 
above  or  below  the  motor  center. 

A  rigid  shaft  in  the  case  of  a  chain-driven  vehicle  would  bind 
unless  the  alignment  was  perfect  and  provision  made  to  prevent 
frame  deflexion,  while  with  a  live  rear  axle  the  shaft  would  bend 
and  bind  in  its  bearings  and  the  whole  transmission  system  would 
be  put  out  of  commission  in  a  short  time.  To  overcome  this,  the 
shaft  which  is  termed  the  drive  or  propeller  shaft  is  made  flexible 

to  a  certain  extent  by 
means  of  universal  joints, 
sometimes  called  Hooke 
or  Cardan  joints. 

These  universal  joints 
serve  the  purpose  of  con- 
necting shafts  whose  axles 
lie  in  the  same  plane,  but 
make  an  angle  with  each 
other    and    are    particu- 
larly required  when  the  angle  varies  between  the  shafts  in  service. 
There  are  various  types  and  perhaps  the  simplest  universal 
joint  consists  of  a  squared  block  secured  to  one  of  the  shafts  to 
be  connected,  fitting  in  a  square  hole  in  a  sleeve  secured  to  the 
other  shaft.    The  four  faces  of  the  block  are  curved  in  the  direc- 
tion of  the  axis  of  the  shaft  to  which  the  block  is  fastened.    This 
type  of  joint  is  shown  in  Fig.  85. 

114 


FIG.  85. 


One   of  the   Simplest  Universal 
Joints. 


UNIVEESAL  JOINT  AND  PKOPELLER  SHAFT     115 


Fig.  86  illustrates  a  somewhat  different  type.     This  consists 
of  six  internal  and  external  teeth;  the  external  teeth  are  curved 
in    the    direction    of    the 
axis  of  the  shaft  and  mesh 
with    teeth   cut    into   the 
housing.    This  joint  is  pro- 
vided with  a  pressed  steel 
cover  and  packing  wash- 
ers to  retain  the  lubricant. 
The  above  types  may  be       FlG>  86>    Universal  with  Internal  and 
properly     termed     align-  External  Teeth, 

ment  joints,  since  they  are 

only  used  between  the  clutch  and  transmission,  when  only  slight 
angular  movement  exists,  Fig.  86  being  the  type  furnished  with 

all  sizes  of  the  well-known 
Hell -Shaw  universal  clutch. 
These  joints  also  constitute 
slip  joints,  since  they  permit 
movement  for  clutch  disen- 
gagement. 

The  cross  type  of  uni- 
versal is  depicted  in  Fig.  87 
and  consists  of  two  forks,  each 
of  which  is  secured  to  one  of 
the  shafts  to  be  connected  to 
each  of  the  forks  by  a  pin. 
In  this  type  of  joint,  the 
axes  of  the  two  pins  do  not  intersect,  but  are  at  some  distance 
from  each  other.  However,  there  is  an  advantage  in  having  the 
pins  both  in  the  same 
plane.  This  end  can  be  at- 
tained in  various  ways  by 
either  using  pins  of  dif- 
ferent diameters  and  pass- 
ing one  through  the  other, 
by  one  long  and  two  short 
pins,  by  forging  the  pins  FlG.  88.  Split-ring  Type  Universal, 
integral  with  a  common 
center  or  forming  them  integral  with  the  forks. 

In  the  joint  shown  in  Fig.  88  the  cross  is  replaced  by  a  split 
ring,  which  carries  the  pin  bearings,  while  the  pins  are  forged 


FIG.  87. 


Cross  Type  Universal  with 
Forks. 


116    MOTOR  TEUCK  DESIGN  AND  CONSTRUCTION 


integral  with  the  forks.  The  ring  is  divided  to  facilitate  assem- 
bling and  thus  permits  the  pins  to  have  their  axes  in  the  same 
plane.  This  type  of  joint  could  also  be  made  by  forming  the  pins 
integral  with  a  central  ring  and  providing  forks  with  separate 
bearing  caps. 

Fig.  89  illustrates  the  Swenson  joint,  which  in  some  respects 
is  similar  to  the  split-ring  type.  It  consists  of  a  fork  with  in- 
tegral pins  and  a  large  pin  passing  through  a  hub  and  supported 


FIG.  89.     Swenson  Universal  Joint. 

by  square  bushings  in  a  ring.  The  integral  pins  are  also  provided 
with  square  bushings  which  fit  into  slots  in  the  ring.  The  bush- 
ings are  held  in  position  by  two  discs  which  together  with  the 
ring  form  a  housing. 

All  universal  joints  are  of  the  pin  type  with  the  exception  of 
the  leather  or  fabric-disc  type,  however,  there  are  various  meth- 
ods used  to  provide  angular  movement.  The  Hartford  joint, 


FIG.  90.     Hartford   Block   and   Trunnion    Type   Joint. 

shown  in  Fig.  90,  is  termed  a  slotted  shell  and  trunnion  type. 
This  consists  of  a  cup -shaped  steel  forging  secured  to  one  of  the 
shafts  with  two  diametrically  opposite  longitudinal  slots  milled 
into  the  shell.  The  other  shaft  is  provided  with  a  ball-shaped 
end,  fitting  the  interior  of  the  shell  and  provided  with  a  pin  ex- 
tending into  the  slots.  Hardened  steel  trunnion  blocks  are  inter- 
posed between  the  pins  and  the  walls  of  the  slots,  to  distribute 
the  bearing  pressure.  This  type  also  serves  as,  a  slip  joint  and  is 
easily  enclosed  with  a  tubular  steel  casing  and  a  leather  boot. 


UNIVEKSAL  JOINT  AND  PROPELLER  SHAFT     117 

Since  this  type  of  joint  permits  endwise  movements  of  the  shaft, 
some  provision  must  be  made  to  hold  the  latter  in  proper  relation 
to  the  two  joints.  Coil  springs  are  used  for  this  purpose. 


FIG.  91.     Evans    Type    of   Block   and   Trunnion   Universal   Joint. 

The  Evans  joint  (Fig.  91)  is  also  of  the  trunnion  type  with 
trunnion  blocks  located  in  diametrically  opposite  slots;  however, 
the  outer  walls  of  these  slots  are  curved  in  the  direction  of  the 
axis  of  the  shaft,  thus  distributing  the  pressure  to  the  three  walls 


FIG.  92.     Detroit  Ball  Bearing  Universal    Joint. 

of  the  slots.  The  pins  which  carry  the  trunnion  blocks  are  forged 
integral  with  the  slip  yoke.  The  joint  is  enclosed  by  a  pressed 
steel  housing  provided  with  a  packing  washer  and  spring  to  re- 
tain lubricant. 


FIG.  93.     The  Hoosier  Universal  Joint. 

In  the  Detroit  universal  joint  shown  in  Fig.  92  the  trunnion 
blocks  are  replaced  by  steel  balls  which  operated  in  a  pressed 
steel  housing  provided  with  diametrically  opposite  slots.  The 
construction  is  similar  to  fig.  89. 


118    MOTOE  TEUCK  DESIGN  AND  CONSTEUCTION 


The  joint  shown  in  Fig.  93  is  sim- 
ilar to  the  block  and  trunnion  type, 
however,  the  yoke  is  provided  with 
diametrically  opposite  slots  and  the  pin 
is  provided  with  square  ends  which  fit 
into  the  slot.  This  pin  is  inserted 
through  a  bushing  in  the  hub  of  the 
joint  which  is  spherical  while  the  hous- 
ing and  yoke  are  also  provided  with 
spherical  surfaces. 

Perhaps  the  most  popular  types  of 
joints  in  use  at  present  are  the  Spicer, 
Arvac,  Hartford  and  Blood  shown  in 
Figs.  94  to  97.  The  Spicer  joint  is  some- 
what related  to  the  ring  type.  It  com- 
prises a  central  ring  with  pins  forged 
integral,  having  their  axis  in  the  same 
plane.  One  forked  end  is  forged  in- 
tegral with  a  hub  which  bolts  to  the  hub 
of  the  permanent  shaft  end,  while  the 
other  fork  may  have  either  a  short  hub 
for  permanent  attachment  to  the  pro- 
peller shaft  or  a  long  hub  to  provide  a 
slip  joint.  The  bearing  ends  of  the  fork 
have  an  opening  large  enough  to  permit 
inserting  the  pins,  while  they  are  also 
bored  out  large  enough  to  take  hard- 
ened and  ground  bushings,  which  hold 
the  ring  and  its  pins  in  position.  These 
bushings  and  fork  ends  have  circular 
grooves  cut  in  them  so  that  a  soft  wire 
can  be  inserted  to  hold  the  bushings  in 
place.  The  mechanism  is  enclosed  in  a 
pressed  steel  housing  which  also  serves  as 
a  retainer  for  the  lubricant. 

The  Arvac  joint  (Fig.  95)  differs 
from  those  depicted  above,  as  it  con- 
sists of  a  ball  yoke  and  socket  fitted 
with  a  cross  block  and  pins  enclosed  in 
a  forged  steel  housing.  This  housing 
supports  two  bushings  which  provide 
the  bearings  for  the  king  pin,  thus  pro- 


UNIVERSAL  JOINT  AND  PKOPELLER  SHAFT     119 


viding  a  light  but  strong  driving  member  of  tubular  section. 
The  bushings  which  fit  into  the  yoke  are  provided  with  shoulders 
and  form  the  bearings  for  the  yoke  pin.  Bushings  are  provided 
with  oil  grooves  and  the  oblong  space  provided  by  the  housing 
forms  grease  pockets,  this  grease  being  oscillated  by  centrifugal 
action  and  this  action  forces  the  lubricant  into  the  oil  grooves  of 


FIG.  95.     Arvac   Universal   Joint   and  Propeller    Shaft  Assembly. 

the  bushings.  The  pins  are  a  press  fit  into  the  cross,  practically 
forming  a  one-piece  driving  member.  The  yoke  end  is  provided 
with  a  spherical  surface  which  with  a  packing  contained  in  a  re- 
tainer forms  a  seal  to  hold  the  lubricant. 

The  Hartford  pin  joint  (Fig.  96)  is  of  the  type  using  one 
long  and  two  short  pins,  and  is  related  to  the  ring  type  in  that  a 
central  ring  is  used  which  carries  the  bushings  that  form  the 
bearings  for  the  pins.  One  fork  end  in  forged  integral  with  a 
hub  which  bolts  to  the  hub  of  the  permanent  shaft  end.  This 
hub  has  lugs  in  the  form  of  a  clevis  so  that  the  load  is  placed  on 


FIG.  96.     Hartford  Pin  Type  Universal  Joint. 

both  ends  of  the  pin  instead  of  at  one  point.  The  long  pin  passes 
through  both  extensions  of  the  yoke  end  and  all  pins  are  held  in 
place  by  washers  and  cotter  pins.  The  mechanism  is  enclosed  in 
a  pressed  steel  housing  provided  with  packing  to  retain  lubricant. 
The  Blood  universal  joint  is  depicted  in  Fig.  97.  This  is  also 
of  the  pin  type,  however,  it  is  of  the  open  construction  since  no 
housing  is  provided.  It  consists  of  a  central  member  in  the  form 


120    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


\/ 


_K 


v/ 


\7 


of  a  cube,  which  is  provided  with  a  large 
and  small  pin,  the  latter  pin  passes 
through  this  cube  and  large  pin  and  is 
locked  in  position  by  a  locking  pin.  The 
two  forks  are  provided  with  bushings  and 
the  outer  ends  of  these  are  enclosed  by 
caps  which  contain  the  lubricant. 

The  universal  joint  assembly  shown 
in  Fig.  98  represents  ~the  type  used  on 
the  military  class  A  and  B  trucks.  It  is 
essentially  a  pin  joint  and  follows  ac- 
cepted practice,  being  provided  with  a 
central  cross  into  which  the  pins  are 
pressed.  In  order  to  form  a  solid  unit 
these  parts  are  locked  by  a  bolt  which 
passes  through  them.  These  pins  pivot 
in  hardened  and  ground-steel  bushings 
which  are  pressed  into  the  fork  and 
flange  yoke.  The  entire  assembly  is  en- 
closed in  a  pressed  steel  housing.  A 
leather  boot  is  attached  to  the  propeller 
shaft  and  this  with  the  housing  forms  the 
grease  retainer. 

These  universals  are  suitable  for 
use  between  the  clutch  and  transmission 
and  the  latter  and  the  rear  axle.  In  com- 
mercial vehicles  two  universals  are  nec- 
essary for  either  location  when  amid- 
ship  mounting  is  provided  for  the  trans- 
mission. In  the  rear  position  one  must 
always  be  provided  with  a  slip  joint  or 
fitting,  while  when  a  slip  joint  is  used 
at  the  front  end  it  compensates  for 
variations  in  shaft  and  frame  lengths, 
clutch  movement  and  is  also  an  advan- 
tage in  assembling.  The  slip  joint  in 
the  rear  must  be  provided  to  compen- 
sate for  variations  in  the  distance  be- 
tween the  axle  and  the  transmission  due 
to  thfe  play  of  the  springs.  This  joint 
may  either  be'  a  square  or  fluted  shaft 
with  a  corresponding  hub  or  sleeve. 


UNIVERSAL  JOINT  AND  PROPELLER  SHAFT    121 


FIG.  98.     Universal  Joint  Used  on  the  Class  B  Military  Trucks. 

Fabric  Joints. — Leather  and  fabric  universal  joints  have  been 
used  for  some  time  because  they  present  several  features  not  ob- 
tainable with  the  mechanical  type.  The  principle  advantages 
are  silent  operation  without  wearing  surfaces  requiring  no  lubri- 
cation. Since  there  is  no  friction  they  are  considered  highly 
efficient  in  the  transmission  of  power.  However,  this  joint  is  not 
adapted  to  conditions  when  there  is  a  great  angularity  between 
shafts  since  the  flexibility  of  the  disc  is  depended  upon  to  com- 
pensate for  this  angular  movement  and  also  the  elongation  in  the 
shaft.  Experience  generally  with  this  type  of  joint  has  not  been 
uniformly  successful  and  extreme  care  is  necessary  in  their  de- 
sign. Owing  to  its  limitations  in  angular  movement  it  is  mostly 
used  between  the  clutch  and  transmission  when  the  angular  move- 
ment is  relatively  small. 

A  typical  joint  of  this  type  for  use  between  clutch  and  trans- 
mission is  shown  in  Fig.  99.  It  consists  of  several  similar  spiders 
usually  three  armed,  fastened  to  the  ends  of  the  shafts  to  be  con- 


FIG.  99.     Thermoid  Fabric-Disc  Type  of  Universal. 

nected  and  of  a  number  of  leather  or  fabric  discs  bolted  between 
the  spiders.  The  arms  of  the  two  spiders  are  staggered  so  that 
any  arm  of  one  of  the  spiders  is  located  midway  between  two 
arms  of  the  other  spider.  Three,  four  or  five  discs  may  be  used 
and  individual  discs  ar6  often  spaced  by  steel  washers. 


122    MOTOE  TRUCK  DESIGN  AND  CONSTRUCTION 


Fabric  discs  are  usually  rubberized.  These  are  built  up  of 
layers  of  fabric  with  the  warp  of  succeeding  layers  at  slightly 
different  angles.  In  fact  the  whole  circle  is  divided  into  a  num- 
ber of  parts  equal  to  the  number  of  layers  in  the  discs  and  the 
angle  thus  arrived  at  is  the  angle  between  the  warp  of  adjacent 
discs. 

Propeller  Shafts. — Propeller  shafts  were  originally  made  of 
solid  section,  however,  with  the  sudden  increase  in  shaft-drive 
construction,  especially  where  the  transmission  was  in  a  unit  with 
the  motor,  came  a  decided  tendency  to  use  either  two  shafts  and 
three  universal  joints,  or  a  large  tubular  shaft  and  two  universal 
joints.  The  advantage  of  the  tubular  lies  in  its  reduced  weight 

and  consequently  the  reduced 
whipping  effect  and  pressure 
on  the  bearings.  A  large  tubu- 
lar shaft  is  shown  in  Fig.  94 
and  a  divided  shaft  of  solid 
section  in  Fig.  97. 

These    tubular    shafts    are 
made    of    40    carbon    seamless 
tubing  and  are  attached  to  stub 
„  „  „  „.-.... .... ,       shaft  which  form  the  connec- 

gr *  i        NXV 

T  :"  7~i  tions  with  the  universal  joints. 

lj  The  ends  of  these  shafts  are 

^- — J  I  m  JK  ->'  ^  jjs*  tJfe^^  generally  made  a  shrink  fit 

into  the  tube  and  then  welded. 
The  manufacturer  of  the  Ar- 
vac  universal  joint  uses  the 
shrink  joint  fit  for  shafts,  but 
these  have  keyways  cut  into 
them  so  that  the  tube  while 
being  shrunk  over  the  shaft 
can  also  be  swaged  into  the 
keyways,  thus  strengthening 
the  welded  joints  in  the  pro- 
peller shaft  and  permitting 
the  driving  strains  to  be  taken 
by  the  swaged  portion  of  the  tube. 

Propeller  Shaft  Mountings. — When  two  shafts  are  used  a  uni- 
versal is  generally  attached  to  the  transmission,  while  the  other 
end  of  the  shaft  is  mounted  in  an  anti-friction  bearing  such  as  a 


FIG.  100.     Lippard  Stewart  Propeller 
Shaft    Mounting. 


UNIVERSAL  JOINT  AND  PKOPELLER  SHAFT     123 

ball  or  roller  bearing.  While  this  divided  propeller  shaft  is  not 
new,  the  use  of  a  tubular  shaft  no  doubt  has  an  influence  on  the 
problem,  and  this  center  bearing  is  receiving  considerable  thought 
at  present,  which  is  evident  through  the  number  of  designs  in  use 
at  present. 

The  construction  shown  in  Fig.  100  consists  of  a  self-align- 
ing ball  bearing  mounted  in  a  housing  which  is  bolted  to  a  cross 
member  of  the  frame.  A  shoulder  on  the  shaft  and  the  hub  of 
the  universal  joint  hold  the  bearing  in  position  while  its  self- 
aligning  feature  and  the  end  play  allowed  in  the  housing  pro- 
vides for  frame  deflexions  and  variations  in  shaft  length. 


FIG.  101.     Globe  Propeller  Shaft  Mounting. 

On  the  Globe  trucks  a  heavy  duty  Hyatt  bearing  is  mounted 
on  a  stub  shaft  welded  to  the  forward  propeller  shaft.  This 
bearing  is  mounted  in  a  bracket  which  is  in  the  form  of  a  hinge. 
This  type  of  mounting  may  be  so  placed  as  to  provide  a  straight- 
line  drive  from  the  transmission  to  the  rear  axle,  since  any  de- 
flexion on  the  side  rails  of  the  frame  may  be  neglected,  due  to  the 
hinged  bracket  providing  the  self-aligning  feature.  The  slip 
joint  is  mounted  as  close  to  the  bearing  as  possible,  as  shown  in 
Fig.  101. 

On  several  models  of  Diamond  T-trucks  four  universals  and 
three  shafts  are  used,  the  center  being  supported  by  two  roller 
bearings  as  illustrated  in  Fig.  102.  Two  slip  joints  are  used,  one 
immediately  back  of  the  transmission  and  the  other  back  of  the 
center  shaft  mounting.  The  bearings  are  Timken  rollers  and 
mounted  in  a  dust-proof  housing  and  provided  with  adjustment. 


124    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


FIG.  102.     Diamond  T  Center  Bearing  Mounting  for  Divided  Propeller 

Shaft. 

On  the  Bethlehem  trucks  the  Barker  floating  bearing  is  used 
which  permits  the  use  of  but  two  universal  joints  and  a  long 
shaft.  .This  is  depicted  in  Fig.  103  and  is  so  mounted  on  the  pro- 
peller shaft  as  to  permit  it  to  float  between  coil  springs.  This 
bearing  has  a  free  movement  up  and  down  with  the  propeller 

shaft  in  one  of  the  slots  of  a  pivoted 
arm.  A  coil  spring  on  the  shank  of 
the  bearing,  which  passes  through  the 
slot  in  the  arm,  slightly  resists  free 
movement  of  the  shaft  away  from  the 
arm,  and  another  coil  spring  at  the  top 
of  the  arm  acts  similar  in  the  opposite 
direction,  the  arm  being  pivoted  at  the 
lower  end.  This  pivot  arm  is  sup- 
ported by  a  bracket  attached  to  a  cross 
member  of  the  frame. 

To  secure  the  highest  efficiency  and 
absence  from  vibration,  care  should  be 
observed  to  have  the  pins  at  opposite 
ends  of  the  assembly  parallel,  as  this 
will  eliminate  vibration  which  may  be- 
come serious  if  the  shaft  whips  as  the 
velocity  of  the  front  joint  must  be  equalized  by  the  rear  joint,  since 
the  velocity  varies  during  each  quarter  revolution.  As  the  bear- 
ing pressures  are  necessarily  high,  proper  means  for  lubrication 
must  be  provided.  The  'assembly  proper  is  usually  provided  with 
a  housing  to  retain  lubricant  and  means  for  inserting  same. 


FIG.  103.  Barker  Propel- 
ler Shaft  used  en  the  Beth- 
lehem Trucks. 


CHAPTER   IX 

THE  DIFFERENTIAL 

ANOTHER  unit  of  the  power  transmission  system  which  must 
be  used  is  the  differential.  It  is  a  well-known  fact  that  in  turn- 
ing a  curve  the  outer  wheels  travel  faster  than  the  inner  ones. 
To  compensate  for  this  a  differential  is  used,  sometimes  called  a 
compensating  or  equalizing  gear. 

If  the  driving  wheels  were  solidly  connected  to  each  other  by 
the  axle  and  that  axle  driven  by  a  chain  or  shaft  from  the  center 
or  thereabouts,  great  stress  would  be  placed  upon  the  transmis- 
sion tires  and  other  parts,  owing  to  the  fact  that  both  wheels  in 
turning  a  corner  would  travel  at  the  same  speed,  but  owing  to  the 
fact  that  the  outside  one  must  travel  faster  than  the  inner  one, 
the  latter  would  be  forced  around  or  skidded  on  the  road. 

The  layman  often  experiences  difficulty  in  understanding  the 
differential,  as  it  is  always  enclosed  in  a  casing  and  is  entirely  out 
of  sight  and  unless  he  has  a  chance  to  see  it  in  the  repair  shop  or 
factory,  he  has  little  chance  to  familiarize  himself  with  its  action 
by  actual  observation. 

The  power  of  the  motor  is  applied  either  to  a  centrally  divided 
rear  axle  (usually  termed  a  live  axle)  or  to  a  jack  shaft,  thence 
by  chains  and  sprockets  to  the  rear  wheels,  turning  loose  on  a 
dead  rear  axle.  The  first  condition  applies  to  all  shaft-driven 
vehicles,  such  as  the  level  gear,  internal  gear,  double  reduction 
and  worm  drive,  the  second  applies  to  chain-driven  vehicles.  The 
action  of  the  differential  is  identical  for  either  of  the  above-men- 
tioned drives.  It  is  mounted  in  the  rear  axle  housing  for  all 
shaft-driven  types,  while  for  the  chain-driven  types  it  is  mounted 
in  the  jack  shaft  housing. 

The  object  of  the  differential  is  to  permit  of  equally  dividing 
the  driving  effort  of  a  single  source  of  motive  power  between  the 
two  driving  wheels  and  to  allow  cars  driven  through  wheels  on 
opposite  sides  to  be  freely  steered.  In  turning  a  corner,  the  driv- 
ing effort  must  be  divided  in  such  a  way  that  one-  wheel  may 
rotate  faster  than  the  other  and  still  receive  the  same  driving 
force  as  the  other.  In  other  words,  the  driving  force  must  be 
equally  divided  between  the  driving  wheels  under  all  conditions 
for  both  forward  and  backward  motion. 

125 


126    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

The  division  of  the  driving  effort  is  very  desirable,  except 
when  the  driving  wheels  are  on  ground  with  greatly  different  co- 
efficient of  adhesion.  For  instance,  if  one  wheel  got  into  a  mud 
hole,  it  might  not  have  sufficient  adhesion  to  prevent  it  from  spin- 
ning under  the  turning  effort  impressed  by  the  differential  gear 
and  it  would  then  be  impossible  to  propel  the  car  except  by  lock- 
ing the  differential,  because  the  turning  effort  of  the  wheel  stand- 
ing on  solid  ground  would  be  no  greater  than  the  turning  effort 
corresponding  to  the  coefficient  of  adhesion  of  the  wheel  in  the 
mud  hole.  For  this  reason  differential  locks  are  often  provided. 


FIG.  104.     Bevel-Gear  Type  Differential. 

This  lock  may  be  left  engaged  as  long  as  all  four  wheels  move 
in  a  perfectly  straight  path.  When,  however,  a  vehicle  is  to  be 
moved  in  a  curved  path  as  in  turning  a  corner  the  driving  wheels 
must  revolve  at  different  speeds,  since  the  outer  one  has  to  cover 
a  longer  distance  in  the  same  time  than  does  the  inner  wheel 
which  is  on  the  inside  of  the  curve. 

There  are  three  types  of  gear  differentials  in  common  use,  viz., 
the  bevel  type,  the  spur  type  and  the  helical  type. 

The  bevel  pinion  type  of  differential,  which  is  probably  the 
most  common  form  is  illustrated  in  Fig.  104.  It  consists  of  the 
following  parts:  a  housing  A,  which  is  usually  made  in  halves, 
two  bevel  gears  B  and  C  secured  to  the  differential  or  driving 
shafts  D  and  E  respectively;  a  two,  three  or  four-armed  spider 
F,  on  the  radial  arms  of  which  are  carried  bevel  pinions  G,  G-l, 
G-%,  G-3  meshing  with  both  of  the  bevel  gears  B  and  G.  To  the 
housing  A  of  the  differential  is  usually  bolted  a  bevel  gear  H  for 
driving  it,  but  this  gear  forms  no  part  of  the  differential  proper. 
It  will  be  understood  that  the  differential  shafts  D  and  E,  either 


THE  DIFFERENTIAL 


127 


have  secured  to  their  outer  ends  road  wheels  or  sprockets,  which 
drive  the  road  wheels  through  chains.  Gear  H  meshes  with  the 
bevel  driving  pinion. 

The  action  of  the  differential  may  be  explained  as  follows: 
The  spider  F  is  held  to  the  housing  A  and  the  turning  effort  or 
torque  which  is  applie'd  to  the  housing  by  means  of  the  driving 
or  ring  gear  //,  and  its  pinion  is  equally  divided  by  the  bevel 
pinion  G  between  the  gears  B  and  C.  As  long,  therefore,  as  the 
resistance  to  motion  of  the  two  bevel  gears  B  and  G  (in  other 
words  to  the  motion  of  the  driving  road  wheels  of  the  car),  is  the 
same,  the  two  wheels  will  turn  at  the  same  speed.  If,  however, 
the  steering  wheel  is  turned  so  as  to  move  the  car  to  one  side  or 
the  other,  the  driving  wheel  on  the  side  to  which  the  car  turns  is 
automatically  held  back  with  a  force  equal  to  the  road  adherence. 
The  differential  gear,  B  or  C  as  the  case  may  be,  on  that  side  will 


FIG.  105.     Spur-Gear  Type  Differential. 

then  turn  slower  and  its  mate  on  the  other  side  will  turn  corre- 
spondingly faster,  while  the  bevel  pinion  G  between  them  will 
turn  on  their  journals  at  a  speed  corresponding  to  the  difference 
in  speed  of  rotation  of  the  two  bevel  gears  B  and  C.  While  a 
vehicle  is  turning  a  curve,  although  the  speeds  of  the  two  driv- 
ing wheels  are  unequal,  the  tangential  forces  acting  at  their  cir- 
cumference are  equal. 

Another  form  of  differential  which  has  been  extensively  used 
is  known  as  the  spur  type  illustrated  in  Fig.  105.  The  action  of 
this  can  be  best  explained  by  comparison  with  the  bevel  type. 
The  bevel  gears  B  and  C  are  here  replaced  by  spur  gears  A  and 


128    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


B  fastened  to  the  differential  shafts  G  and  D  respectively.  While 
the  inner  sides  of  the  hubs  of  these  spur  gears  come  close  to- 
gether, the  inner  edges  of  the  gears  themselves  are  at  some  dis- 
tance apart.  Meshing  with  these  two  spur  gears  A  and  B  are 
two,  three  or  four  sets  of  spur  pinions,  E,  F.  These  spur  pinions 
have  a  width  of  face  almost  twice  that  of  the  spur  gears  A  and  B. 
The  outer  portion  of  the  face  of  each  pinion  meshes  with  one  of 
the  spur  gears,  and  the  inner  portions  of  the  faces  of  the  pinions 
mesh  together.  It  will  be  readily  understood  that  if  the  casing 
of  the  differential  G  is  held  stationary  and  the  spur  gear  is  re- 
volved by  hand  or  otherwise  in  a  clockwise  direction,  the  pinion 
E  meshing  with  it  is  revolved  in  a  counter-clockwise  direction :  the 
pinion  F  meshing  with  E  is  revolved  in  a  clockwise  direction  and 
the  gear  B  is  revolved  in  a  counter-clockwise  direction.  That  is, 
gear  B  is  rotated  in  an  opposite  direction  to  gear  A,  exactly  as 

with  the  bevel  gear  dif- 
erential.  In  regular  op- 
eration the  turning  effort 
is,  of  course,  transmitted 
to  the  differential  housing 
by  means  of  gears  and 
the  turning  effort  thus  re- 
ceived by  the  housing  is 
equally  divided  by  the 
sets  of  spur  pinions  be- 
tween the  spur  gear  A  and 
B,  that  is,  between  the  two 
driving  road  wheels.  The 
properties  of  the  spur- 
gear  differentials  are  ex- 
actly the  same  as  those  of 
the  bevel-gear  differential. 

The  problem  of  working  out  a  neat  and  all  around  satis- 
factory differential  lock  for  either  of  the  above  types  presents 
considerable  difficulty,  which  is  probably  the  reason  that  this 
device  is  not  more  extensively  used.  Fig.  106,  this  lock  which 
is  in  the  form  of  a  four- jaw  clutch,  one  member  being  keyed  to 
the  drive  shaft  and  free  to  slide  upon  it,  while  the  other  is  keyed 
to  the  differential  case.  Meshing  the  two  clutch  members  locks 
the  differential,  since  one  shaft  is  locked  against  the  other  through 
the  differential  housing. 


FIG.  106. 


A  Neat  and  Simple  Differen- 
tial Lock. 


THE  DIFFERENTIAL  129 

A  differential  lock  can  also  be  provided  with  the  spur  type 
and  an  excellent  example  is  illustrated  in  connection  with  Fig. 
105.  A  large  flange  is  so  mounted  on  the  differential  housing 
that  it  can  be  moved  endwise,  and  the  stud  of  one  of  the  spur 
pinions  extends  beyond  the  housing.  Half  of  the  end  of  this  stud 
is  milled  off  so  that  the  sliding  member  can  be  moved  in,  thus 
preventing  the  pinion  from  turning,  which  locks  the  entire  dif- 
ferential. 

The  ordinary  type  of  differential  mentioned  above  presents 
certain  disadvantages,  the  principal  objection  being  that  it  pro- 
motes skidding.  Recently  several  designs  of  differentials  have 
been  developed  in  which  this  common  objectionable  feature  has 
been  eliminated.  This  type  is  known  as  the  helical  gear  type. 

In  the  Powrlok  device,  there  are  two  or  more  pinions  mounted 
in  the  differential  housing  which  is  rotated  by  the  engine,  and 
also  two  crown  wheels  are  attached  to  either  driving  wheel.  But, 
in  addition,  there  are  worm  gears  interposed  between  the  pinions 
and  the  crown  wheels,  the  teeth  on  which  are  shaped  to  corre- 
spond. These  worms  are 
mounted  in  the  differential 
casing  as  shown  in  Fig.  107 
with  their  axis  at  right  angles 
to  those  of  the  pinions.  It 
will  be  seen,  then,  that  the  ro- 
tation of  the  differential  hous- 
ing in  the  usual  way  causes 
FIG.  107.  Powrlok  Differential.  both  pinions  and  worm  gears 

to  be  carried   around  bodily 

in  rigid  relation  to  each  other,  whilst  at  the  same  time  both  pin- 
ions and  worms  have  a  power  of  rotation  upon  their  own  axis,  so 
that  they  can  be  moved  rotationally,  but  not  bodily,  in  relation 
to  each  other. 

When  road  resistance  is  sufficient  to  give  adhesion  to  each 
driving  wheel,  both  wheels  are  equally  driven,  the  crown  wheels 
to  which  they  are  attached  being  carried  bodily  round  by  the 
worms  in  which  they  are  in  engagement,  just  as,  with  an  ordinary 
differential,  they  are  carried  round  by  the  pinions.  But  when 
road  resistance  upon  one  wheel  is  reduced  to  a  point  at  which  it 
loses  adhesion,  and  would,  with  the  ordinary  differential,  start 
spinning,  nothing  of  this  kind  .happens,  because  the  angle  of  the 
worms  is  such  that  whilst  the  crown  wheels  can  drive  the  worms, 
10 


130    MOTOE  TEUCK  DESIGN  AND  CONSTEUCTION 

the  worms  cannot  drive  the  crown  wheels,  and,  as  a  consequence, 
the  differential  is  locked  so  far  as  any  movement  of  the  wheel  in 
relation  to  the  differential  is  concerned.  The  axle  becomes  for  all 
practical  purposes  a  solid  one,  and  all  the  drive  is  taken  by  the 
wheel,  which  is  for  the  moment  supported  on  firm  ground  and 
can  take  advantage  of  its  grip. 

When  both  wheels  are  on  firm  ground  and  the  vehicle  is  trav- 
eling freely,  the  differential  is  enabled  to  act  in  the  usual  manner 
when  turning  corners,  by  reason  of  the  fact,  already  alluded  to, 
that  the  crown  wheels  can  drive  the  worms.  Each  driving  wheel 
is  attached  to  its  respective  crown  wheel,  and  when  a  curve  in  the 
road  is  followed,  the  outer  wheel  is  forced  by  its  contact  with  the 


m 
•is 


FIG.  108.     Exterior  of  the  Walter  Differential. 

road  to  travel  a  greater  distance  than  the  inner  one.  The  outer 
wheel,  therefore,  revolving  faster  than  the  axle,  turns  the  worm 
in  connection  with  it  and  so  enables  the  central  pinions  to  act  and 
react  on  the  worms  with  a  differential  action  and  to  distribute  the 
power  to  each  wheel  in  the  usual  manner. 

The  Walter  differential  (Fig.  108)  is  also  of  the  irreversible 
worm-gear  type,  which  drives  both  wheels  regardless  of  the  trac- 
tion conditions  of  the  other  wheel  and  which  still  has  a  compen- 
sating differential  action.  It  consists  of  two  pairs  of  spiral  gears 
mounted  in  a  two-part  housing,  and  meshing  together  and  sep- 
arately with  worms  in  the  housing  and  on  the  drive  shafts.  Both 
halves  of  the  housing  are  alike  except  for  the  bevel  or  ring-gear 
flange.  The  two  bolts  which  bolt  the  housing  together  set  one- 
half  ahead  of  the  other  so  that  the  spiral-gear  pairs  mesh  directly 
together. 


THE  DIFFERENTIAL'  131 

The  operation  of  this  device  is  as  follows:  The  driving  re- 
sistance of  the  road  wheels  tends  to  rotate  the  spiral  gears  on 
their  pins,  but  in  opposite  directions,  but  if  one  road  wheel  has  a 
greater  resistance  the  inequality  of  force  cannot  drive  the  other 
wheel  faster  as  the  spiral  gear  cannot  drive  the  worm,  so  both 
wheels  are  positively  driven.  When  turning  the  outer  wheel 
rolls  faster  and  so  permits  the  inside  wheel  to  turn  correspond- 
ingly slower,  giving  a  compensating  differential  action. 

Lately  there  has  been  a  tendency  to  substitute  an  equalizing 
gear  for  the  differential  which  to  certain  extent  eliminates  its 
disadvantages,  since  this  equalizing  device  can  be  so  arranged  as 
to  limit  the  pull  on  one  wheel  to  the  amount  required  to  slip  the 
other.  However,  as  the  use  of  these  has  been  limited  to  low- 
powered  passenger  cars  they  will  not  be  considered  in  this  chapter. 

When  all  four  wheels  of  a  vehicle  are  used  as  driving  wheels, 
it  is  generally  necessary  to  provide  three  differentials ;  one  in  the 
transmission  case  to  equally  divide  the  turning  effort  between 
each  pair  of  driving  wheels  and  one  for  each  front  and  rear  drive. 

Thus  the  differential  is  absolutely  necessary  in  any  form  of 
final  drive  used  on  commercial  vehicles  and  it  presents  consid- 
erable advantages  in  protecting  all  parts  of  the  mechanism  against 
stress  when  turning  corners.  While  it  also  has  the  disadvantage 
of  stalling  a  vehicle  when  one  wheel  gets  into  a  mud  hole. 

This  disadvantage  may  be  overcome  by  providing  a  differ- 
ential lock,  this  again  places  the  responsibility  upon  the  operator 
and  should  he  attempt  to  round  a  curve  with  the  differential 
locked,  the  tires  and  driving  mechanism  would  be  subjected  to 
considerable  wear.  Should  this  be  done  quite  frequently,  the 
results  would  soon  be  noticeable. 

In  order  to  overcome  the  latter  feature,  this  lock  is  operated 
by  a  foot  pedal  and  so  arranged  that  it  must  always  be  held  in 
engagement.  Removing  the  foot  pressure  disengages  the  lock, 
thus  providing  for  the  poor  memory  of  the  operator. 


CHAPTER   X 

THE  FINAL  DRIVE 

Chain,  Bevel,  Double  Reduction,  Internal  Gear  and  Worm 
Drive. — From  the  transmission  the  power  must  be  transmitted  to 
another  unit  from  which  it  is  converted  into  useful  work  at  the 
road  wheels.  In  commercial  car  construction  this  is  generally 
termed  the  final  drive.  There  are  a  variety  of  methods  of  trans- 
mitting the  power  and  in  taking  up  the  discussion  of  the  final 
drive,  the  writer  will  attempt  to  cover  this  subject  as  clearly  as 
possible  and  is  offering  illustrations  of  a  number  of  different 
types  in  use  at  present.  The  general  problem  of  the  final  drive 
resolves  itself  into  the  transmission  of  motion  from  one  or  more 
revolving  shafts  to  driving  wheels  flexibly  connected  to  the  frame 
through  axle  and  springs,  and  at  the  same  time  effecting  a  reduc- 
tion in  rotative  speed  between  the  driving  shaft  and  rear  wheels. 

Chain  Drive. — During  the  past  years  the  majority  of  commer- 
cial cars  were  equipped  with  what  is  known  as  the  double  side- 
chain  drive.  The  principal  objection  to  it  is  the  attention  re- 
quired to  obtain  maximum  efficiency.  It  is  generally  exposed  and 
dirt  soon  finds  its  way  into  the  numerous  bearings,  causing  rapid 
wear.  For  a  time,  chain  cases  seemed  to  be  the  solution  of  the 
problem,  but  they  are  not  satisfactory  and  most  makers  started 
experimenting  with  different  types  of  shaft  drives.  This  has 
resulted  in  the  introduction  of  the  bevel  gear,  double  reduction, 
internal  gear  and  worm  gear  rear  axles. 

In  chain  drive  the  power  must  be  transmitted  to  a  unit  carry- 
ing the  driving  sprockets,  the  differential  and  in  some  cases  a  set 
of  brakes.  This  unit  is  generally  termed  the  jack  shaft  and  may 
be  built  integral  with  the  transmission  or  in  a  separate  unit, 
mounted  separately  or  bolted  to  the  transmission.  This  jack 
shaft  is  similar  to  and  performs  the  same  functions  the  bevel  gear 
rear  axle  in  pleasure  cars,  excepting,  of  course,  that  it  does  not 
carry  the  weight  of  the  vehicle.  For  this  purpose  a  dead  rear 
axle  is  used,  which  has  spindles  upon  which  the  wheels  and  their 
bearings  are  mounted.  Various  types  of  rear  axles  may  be  found 
in  use  at  present,  their  section  being  either  round,  square,  rectan- 
gular or  I-beam.  The  jack  shaft  is  usually  equipped  with  one  set 

132 


THE  FINAL  DRIVE 


133 


of  brakes,  while  the  other  set  is  mounted  in  the  rear  wheels. 
However,  some  makers  mount  both  sets  of  brakes  on  the  rear 
wheels. 

Some  method  must  be  provided  to  take  up  the  driving  thrust 
from  the  rear  axle  to  the  frame.  For  this  purpose  a  radius  rod 
is  provided,  which  also  takes  up  the  brake  pull,  and  the  reaction 
due  to  chain  pull,  as  well  as  allowing  for  adjusting  the  slack  in 
the  chain.  These  rods  are  generally  of  the  full  universal  type, 
being  pivoted  on  the  jack  shaft  and  the  brake  support  or  spindle 
of  the  rear  axle.  They  are  sometimes  provided  with  large  coil 
springs  to  take  up  abnormal  shocks,  when  engaging  the  clutch  or 
backing  up  to  a  curb. 

The  chain  drive  in  reality  is  a  double  reduction  through  two 
units,  one  reduction  being  obtained  through  the  bevel  gears  in 
the  jack  shaft,  while  the  other  is  obtained  through  the  jack  shaft 
and  rear  wheel  sprockets. 


fiAV/US 

ftOO 
CONNECTION 


FIG.  109.     Sheldon  Jack  Shaft. 

Fig.  109  illustrates  the  jack  shaft  built  by  the  Sheldon  Axle 
and  Spring  Company,  which  was  used  on  a  number  of  commer- 
cial cars,  being  a  separate  unit  so  arranged  that  a  standard  trans- 
mission may  be  bolted  to  it.  The  differential  is  of  the  bevel-gear 
type,  while  the  working  parts  are  mounted  on  ball  bearings. 

Fig.  110  depicts  the  Velie  jack  shaft  which  is  a  separate  unit, 
the  transmission  being  mounted  on  a  sub-frame,  while  the  jack 
shaft  is  mounted  on  the  main  frame.  Like  the  Sheldon  construc- 
tion, the  driving  unit  is  so  arranged  that  it  may  be  removed 
through  the  inspection  cover  opening  without  removing  the  jack 
shaft  unit  from  the  chassis.  The  differential  lock  is  also  shown, 
mounted  on  the  right  side  of  the  differential  housing.  The  jack 
shaft  is  flexibly  mounted  on  the  frame,  while  a  torque  arm  is  used 
to  hold  it  in  alignment.  The  differential  and  drive  shafts  are 
mounted  on  roller  bearings.  Internal  expanding  brakes  are  pro- 


134    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


THE  FINAL  DRIVE 


135 


vided.     The  outboard  bearing  for  the  sprocket  is  mounted  as 
close  as  possible  to  the  chain  center,  so  as  to  overcome  the  high 
tension  in  the  chain  on  low 
gear. 

In  Fig.  Ill  is  shown 
the  Velie  rear  axle  which 
is  of  round  section,  hav- 
ing a  spring  seat,  which 
also  carries  the  brake 
spider  keyed  to  it  by  a 
large  bolt.  The  spring  is 
mounted  above  the  axle 
and  retained  by  spring 
clips.  The  radius  rod  is 
mounted  inside  of  the 
spring  and  pivots  on  the 
rear  axle  spindle.  Inter- 
nal expanding  brakes  are 
mounted  inside  the  brake 
drum,  to  which  the  driv- 
ing sprockets  are  attached. 
This  drum  is  attached  to 
the  spokes  of  the  wood 
wheel  by  spoke  clips,  while 

the  wTheels  are  equipped  with  dual  tires.     Wheels  have  roller 
bearings. 

Fig.  112  illustrates  the  radius  rod  used  on  the  Atterbury  chain- 
driven  models.  This  rod  is  of  the  universal  type,  being  pivoted 
and  hinged  to  jack  shaft  at  the  forward  end  and  hinged  to  the 


FIG.  111.     Velie  Eear  Axle. 


BRAKE  SUPPQ&T 
RADIUS  ROD 


FIG.  112.     Atterbury  Eadius  Eod. 


136    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

brake  support  at  the  rear  end,  which  in  turn  is  found  to  pivot  on 
the  rear  axle  spindle.  An  adjustment  is  provided  at  the  forward 
end  on  which  is  mounted  a  heavy  coil  spring.  The  rod  is  con- 
structed in  two  sections,  so 
that  the  rear  end  may  slide 
upon  the  forward  end,  the 
spring  holding  both  ends 
in  their  positions.  When 
the  clutch  is  suddenly  en- 
gaged or  when  backing  up 
to  a  curb,  this  spring  takes 
up  the  abnormal  shock  by 
compressing  and  permit- 
FIG.  113.  Peerless  Jack  Shaft  Intregal  ting  the  rear  section  to  slide 
with  Transmission.  over  the  forward  one.  As 

soon  as  the  force  is  re- 
moved the  spring  expands  and  returns  the  rear  end  to  its  proper 
position.  This  type  of  radius  rod  is  also  used  on  the  Velie  and 
Lewis  commercial  cars. 

Oil  the  Peerless  truck,  the  jack  shaft  is  built  integral  with  the 
transmission  as  shown  in  Fig.  113.  It  is  similar  to  the  construc- 
tion described  above,  excepting  that  one  set  of  brakes  is  mounted 
on  the  jack  shaft  inside  of  the  frame  and  anchored  to  the  frame 
cross-member  instead  of  to  the  housing  proper.  The  shafts  are 
not  enclosed,  but  are  mounted  in  anti-friction  bearings  attached 
to  the  frame.  With  this  construction  the  brakes  are  better  pro- 
tected from  mud  and  water.  Construction  of  this  type  may  also 
be  found  on  several  other  cars. 

The  Vulcan  radius  rod  and  rear  axle  construction  differ  some- 
what from  the  above  in  that  the  radius  rod  adjustment  is  placed 
at  the  rear  instead  of  the  customary  place  near  the  jack  shaft 
sprocket.  By  referring  to  Fig.  114,  it  will  be  noted  that  the 
radius  rod  proper  is  similar  to  a  marine  engine  connecting  rod 
with  caps  bolted  to  the  jack-shaft  end  which  fit  over  a  spherical 
bearing.  The  rear  end  has  three  bosses,  through  which  are  in- 
serted two  guide  pins  and  an  adjusting  screw.  These  guide  pins 
are  retained  by  clamping  bolts,  while  the  adjusting  screw  is  at- 
tached to  a  yoke,  through  the  outer  ends  of  which  the  guide  pins 
pass.  A  large  bolt  passes  through  the  heads  of  these  and  through 
a  bracket  which  pivots  on  the  axle  spindle,  formed  integral  with 
the  brake  support.  The  hub  and  brake  drum  are  cast  integral 


THE  FINAL  DRI\TE 


137 


and  attached  to  the  wheel  by  bolts  and  the  wheels  are  mounted  on 
roller  bearings. 


FIG.  114.     Vulcan  Eadius  Eod  with  Adjustment  at  Eear  End. 

The  Kelly  jack  shaft  (Fig.  115)  illustrates  a  pressed  steel 
housing  and  a  full  floating  construction  which  is  quite  accessible. 
The  housing  proper  is  pressed  in  two  halves  and  welded  together, 
while  reinforcing  tubes  and  flanges  are  used  to  strengthen  it.  To 
this  pressed  steel  jack-shaft  housing  is  bolted  a  cast  steel  differ- 
ential carrier  or  housing  which  carries  the  entire  differential  as- 
sembly and  also  the  transmission.  Provision  is  made  for  inspec- 
tion of  the  differential  assembly  by  removing  the  pressed  steel 
cover  from  the  rear  of  the  jack-shaft  housing.  Each  end  carries 
a  supporting  roller  bearing  mounted  in  sleeves  and  held  in  place 
by  the  carrier  and  caps.  An  adjusting  nut  screws  over  each 
sleeve,  where  it  is  easily  accessible  and  is  locked  by  a  small  key 
on  the  carrier  cap. 


138    MOTOK  TRUCK  DESIGN  AND  CONSTRUCTION 

The  outer  end  of  the  jack-shaft  housing  terminates  in  ball 
sleeves,  which  are  riveted  to  it.  These  sleeves  provide  universal 
movement  for  the  entire  unit  when  mounted  in  the  chassis  frame 
and  also  a  universal  movement  for  the  forward  end  of  the  radius 


CARRIER 
L  HOU5IN6 

HOUSING  REINFORCING  FLAME 
AND  TUBE 


FIG.  115.     Kelley-Springfield  Floating   Jackshaft  with  Pressed   Steel 

Housing. 

rod.  The  ball  sleeves  accommodate  a  roller  bearing  held  in  posi- 
tion against  the  shoulder  of  the  drive  shaft  by  a  large  lock  nut 
properly  secured  by  lock  wires.  A  large  adjusting  nut,  contain- 
ing a  felt  washer  screwed  into  the  end  of  the  ball  sleeve,  bears 
against  the  outer  race  of  the  bearing.  Sprockets  are  bolted  to  the 
flanges  forged  integral  with  the  drive  shafts  and  the  bolts  are 
equipped  with  hardened  steel  bushings.  They  afford  equal  dis- 
tribution of  the  shearing  strains  on  the  bolts,  due  to  the  drive  of 
the  truck. 


FIG.  116.     Kelley  Radius  Eod,  Brake  and  Rear  Axle  Construction. 


THE  FINAL  DRIVE 


139 


Fig.   116  illustrates  the  radius  rod  and  double  rear  wheel 

& 

brakes  of  the  Kelly  trucks.  The  radius  rod  proper  is  a  drop 
forging  and  pivots  from  the  brake  spider.  The  chain  adjustment 
is  incorporated  at  the  front  end  by  adjusting  screws.  The  rear 
axle  is  of  I-beam  section  with  integral  spring  pads. 


FIG.  117.     G.M.C.  Eadius  Rod  and  Eear  Construction. 

The  G.M.C.  one-,  one-and-a-quarter  and  two-ton  models  have 
similar  constructions  excepting  for  size,  which  varies  on  the  dif- 
ferent capacities.  This  is  illustrated  in  Fig.  117,  showing  the 
two-ton  construction.  The  rear  axle  is  of  rectangular  section 
and  has  a  long  spindle  upon  which  the  spring  seats,  brake  spider 
to  which  the  radius  rod  body  is  riveted  and  the  wheels  are 
mounted.  The  hub  and  brake  drum  for  the  internal  brake  are 
formed  integral,  while  a  separate  brake  drum  is  attached  to  the 
wheel  spokes  for  the  external  brake,  both  sets  of  brakes  being 
mounted  in  wheels  operating  on  separate  drums.  The  radius  rod 
has  the  brake  shaft  bearings  riveted  to  it,  so  that  all  brake  reac- 
tions are  taken  on  the  radius  rod.  This  radius  rod  is  divided  into 
a  front  and  rear  part,  each  having  a  large  threaded  boss  to  re- 
ceive the  adjusting  screw.  This  screw  has  right  and  left-hand 
threads  and  is  locked  by  lock  nuts.  The  front  end  of  the  rod  is 
divided  on  the  jack-shaft  center  and  is  provided  with  a  spherical 
surface  to  give  universal  movement. 


140    MOTOE  TRUCK  DESIGN  AND  CONSTRUCTION 

An  enclosed  chain  drive  is  illustrated  in  Fig.  118.  This  con- 
struction has  been  used  on  the  Natco  one-ton  trucks  for  several 
years.  The  case  is  cast  in  two  parts  and  well  ribbed,  so  that  it 
can  be  used  as  the  radius  rod  also.  The  forward  end  carries  the 
adjusting  member,  which  is  in  the  form  of  an  eccentric  and  pro- 


ECCENTRIG  ADJ.    MEMBER. 


FIG.  118.     Enclosed  Chain  Drive. 

vides  a  spherical  bearing  to  obtain  universal  action.  The  rear 
end  pivots  about  the  brake  drum,  in  which  are  mounted  double 
expanding  brakes.  The  rear  wheel  hub  and  brake  drum  are  cast 
in  one  piece  to  obtain  proper  strength  for  this  construction,  since 
the  thrust  is  transmitted  through  the  brake  drum.  Ground  joints 
are  used  to  prevent  oil  leaks,  while  drain  plugs  are  also  provided 
so  that  the  case  can  be  cleaned  at  intervals. 

The  advantages  of  the  chain  drive  are  low  cost  of  changing 
gear  ratios,  minimum  unspring  weight,  somewhat  greater  flexibil- 
ity, mounting  of  differential  on  chassis,  where  it  is  protected  by 
the  vehicle  springs,  and  greater  accessibility,  for  broken  links  can 
be  repaired  easily.  When  it  is  kept  clean,  oiled  and  properly  ad- 
justed it  is  a  very  efficient  means  of  power  transmission ;  however, 
this  is  quite  a  difficult  problem.  This  naturally  suggests  enclosed 
chain  drives  which  operate  in  oil ;  however,  a  practical  chain  case 
is  a  difficult  problem,  so  that  many  joints  and  bearings  are  nec- 
essary, which  are  subject  to  frequent  renewal  and  in  service  the 
chain  case  soon  becomes  more  noisy  than  the  open  drive.  It  also 
makes  a  somewhat  inaccessible  construction,  thus  increasing  main- 
tenance cost. 

The  Bevel-gear  Axle. — The  bevel-gear  axle  is  almost  univer- 
sally used  on  pleasure  cars.  However,  it  is  not  very  popular  on 
commercial  cars,  being  used  only  on  the  light  vehicles  of  capaci- 
ties up  to  1,500  Ibs.  Its  use  is  limited,  owing  to  that  it  is  very 


THE  FINAL  DRIVE 


141 


difficult  to  provide  a  higher  reduction  than  four  or  five  to  one 
without  sacrificing  road  clearance. 

Fig.  119  depicts  the  G.M.C.  1,500-lb.  delivery  car  bevel  drive 
rear  axle,  which  is  of  the  three-quarter  floating  type.  The  axle 
housing  is  divided  into  two  halves  having  tubes  riveted  into  it, 
wThich  extend  slightly  beyond  the  wheel  bearing.  The  differential 
is  of  the  bevel-gear  type  and  mounted  on  Hyatt  roller  bearings 


TUBE  YOKE 


FIG.  119.     G.M.C.  Delivery   Car  Bevel  Gear  Type  Rear  Axle. 

inside  of  the  axle  housing.  Ball  thrust  bearings  with  ample  ad- 
justment are  mounted  on  each  side  of  the  Hyatt  roller  bearings 
to  take  up  the  thrust  load  of  the  gears.  The  hub  is  provided  with 
a  Hyatt  bearing,  which  is  centered  under  the  wheel  and  is  re- 
tained by  a  threaded  retaining  member  which  has  a  funnel-shaped 
part  formed  integral  to  throw  off  the  oil  and  prevent  it  from 
reaching  the  brakes.  The  hub  is  keyed  to  axle  shaft,  so  that  the 
weight  is  carried  on  the  housing  tube,  while  the  shaft  transmits 
the  powder.  The  spring  seat  swivels  upon  the  brake  spider,  which 
also  carries  the  ends  of  the  truss  rod.  The  axle  housing  has  a 
bracket  to  support  the  brake  shafts,  so  that  the  levers  can  be 
mounted  close  to  the  center  of  the  axle.  The  brakes  are  of  the 
internal  and  external  type  and  operate  on  pressed  steel  brake 
drums  bolted  to  the  wheels..  The  propeller  shaft  is  enclosed  in 
the  torque  tube,  which  is  bolted  to  the  axle  housing  and  carries 
the  ball  bearings  for  supporting  the  bevel  pinion,  while  the  pin- 


142    MOTOE  TRUCK  DESIGN  AND  CONSTRUCTION 

ion  shaft  and  the  propeller  shafts  have  squared  ends  and  are  con- 
nected by  a  sleeve  having  a  square  hole  fitting  over  the  squared 
shaft  ends. 

The  torque  is  taken  by  the  torque  tube  through  a  large  fork, 
which  is  hinged  to  a  heavy  cross  member,  while  the  spring  is  free 
at  both  ends.  Radius  rods,  running  from  the  brake  spider  diag- 
onally to  a  point  directly  back  of  the  torque  tube  fork,  take  up 
the  thrust  load. 

Bevel  gear  drive  axles  of  similar  construction  are  also  on  the 
Steward,  Commerce,  Vim  and  other  light  delivery  cars.  They 
are  mostly  used  with  pneumatic  tires,  where  speed  is  a  factor. 

Types  Intended  to  Overcome  Reduction  Difficulties. — The  dif- 
ficulty with  the  bevel-gear  axle  is  overcome  in  the  double  reduc- 
tion, internal  gear  and  worm-gear  axles.  The  double  reduction 
and  the  internal  gear  type  use  two  reductions,  one  by  bevel  gears 
and  the  other  by  spur  gears,  while  in  the  worm-gear  axle  a  large 
reduction  can  be  obtained  with  a  single  pair  of  gears. 

The  advantages  claimed  for  the  double  reduction  are  silent 
operation,  enclosure  of  all  working  parts,  while  the  differential 
bearings  are  relieved  of  thrust  loads.  By  mounting  one  pair  of 
gears  above  the  other,  approximately  straight-line  drive  can  be 
obtained. 

The  internal  gear-drive  axle  possesses  the  advantages  of  silent 
operation  and  enclosed  working  parts.  However,  the  differential 
bearings  are  subjected  to  thrust  loads,  since  the  spur  gears  are 
mounted  in  the  wheel,  and  it  is  also  difficult  to  obtain  a  straight- 
line  drive.  They  possess  an  advantage  in  that  this  axle  is  divided 
into  two  units,  the  jack  shaft  which  transmits  the  power  and  the 
dead  rear  axle  which  carries  the  weight.  The  jack  shaft  is  sim- 
ilar to  the  chain  drive  jack  shaft  and  may  either  be  bolted  to  the 
front  or  rear  of  the  dead  axle. 

The  worm-gear  axle  is  probably  the  most  simple  construction, 
since  it  has  the  least  number  of  parts,  can  easily  be  arranged  for 
straight-line  drive,  and  possesses  the  features  of  silent  operation, 
protection  of  parts  subject  to  wear  and  a  wide  range  of  gear 
ratios  can  be  provided  without  changing  the  distance  between 
the  worm  and  the  wheel. 

All  types  of  shaft- driven  axles  can  be  made  quite  accessible 
so  that  maintenance  can  be  held  within  reason.  The  double  re- 
duction and  worm-gear  axles  are  generally  of  the  full  floating 
type,  in  which  the  weight  is  carried  on  the  axle  tubes  and  the 
shafts  are  subject  to  only  torsional  stresses,  as  they  only  transmit 
power. 


THE  FINAL  DRIVE 


143 


The  Double-reduction  Axle. — One  of  the  first  commercial  car 
builders  to  use  a  shaft-drive  axle  was  the  Autocar  Company, 
which  equips  all  of  its  models  with  double-reduction  axles.  Ex- 
tensive refinements  have  been  made  on  this  axle  and  it  presents  an 


FIG.  120.     Double  Reduction  Axle  used  on  the  Autocar. 

excellent  type  of  double  reduction.  This  axle  is  shown  in  Fig. 
120,  and  is  what  is  termed  a  full-floating  axle.  The  bevel  gears 
are  placed  above  the  spur  gears  so  that  a  straight  drive  can  be 


FIG.  121.     Weston-Mott  Double  Reduction  Axle. 

obtained,  while  it  also  has  an  advantage  in  machining  the  bevel 
gears,  since  they  are  much  smaller  than  they  would  be  if  they 
were  used  instead  of  spur  gears  for  the  final  reduction.  The  spur 
gears  are  better  able  to  take  care  of  the  torque  of  the  second  re- 
duction and  the  differential  bearings  are  relieved  of  the  high 


144    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

thrust  loads,  which  they  would  be  required  to  carry  if  bevel  gears 
were  used. 

The  axle  housing  proper  is  cast  in  two  halves  joined  together 
at  the  center.  The  spring  seats  are  cast  integral  and  the  end  of 
the  housing  is  provided  with  a  flange  to  which  the  brake  spider 
is  bolted.  A  reinforcing  tube  is  placed  into  the  housing,  which 
extends  a  little  beyond  the  spring  seat,  the  end  of  which  carries 
the  wheel  bearings.  The  bevel  and  spur  driving  gear  and  dif- 
ferential are  mounted  in  a  unit  in  the  differential  carrier  and 
bolted  to  the  housing  proper.  The  drive  shafts  have  splined 
ends  and  the  wheel  drive  is  taken  through  flanges  bolted  to  the 
hub.  Internal  and  external  brakes  are  mounted  on  the  brake 
drums  inside  of  the  wheels. 


FIG.  122.     White   1J   Ton  Double  Reduction  Axle  with  Helical  Cut  Spur 

Gears. 

Fig.  121  illustrates  a  double-reduction  axle  of  one-ton  capacity, 
which  was  placed  on  the  market  several  years  ago  by  the  Weston 
Mott  Company,  and  was  used  on  the  Menominee,  Flint  and  other 
light  commercial  cars.  This  axle  is  also  of  the  full  floating  type, 
but  differs  from  the  one  described  above  in  that  straight-line 
drive  cannot  be  obtained  since  the  bevel  gear  set  is  mounted  in 
front  of  the  spur  gear  set  instead  of  above  it.  The  differential 


THE  FINAL  DRIVE 


145 


f 


carrier  has  an  extension  on  each  side  into  which  are  placed  the 
axle  tubes,  while  a  large  cover  is  provided  for  inspection  pur- 
poses. The  brake  spider  has  a  hub  which  is  keyed  to  the  axle 
tube  and  upon  which  the  spring  seat  can  pivot,  while  the  brake 
operating  levers  are  also  brought  inside  of  the  frame.  The  drive 
for  the  wheel  is  through  a  jaw  clutch,  the  male  member  of  which 
is  forged  integral  with  the  drive  shaft,  while  the  female  member 
is  formed  integral  with  the  hub. 

The  Autocar  is  designed  to  take  both  torque  and  thrust 
through  the  spring,  while  the  Weston  Mott  axle  may  be  arranged 
•with  radius  rods  to  take  the  thrust  load  and  a  torque  arm  to  take 
the  torque  load. 

The  one-and-one-half  ton  White  truck  is  also  equipped  with 
a  double-reduction  axle  (Fig.  122)  which  differs  from  the  above 
in  that  the  bevel  gears  are  in  the  customary  place  as  in  the  pleas- 
ure car  axle.  The  propeller  shaft  carrying  the  spur  pinion  which 
has  helical  teeth,  is  mounted  above  the  short  shaft  carrying  the 
helical  spur  gear  and  bevel  pinion.  Both  shafts  are  supported  by 
ball  bearings  at  each  end  and  provision  is  made  to  take  care  of 
the  thrust  of  these  gears.  This  presents  another  method  of  ap- 
proximately a  straight-line  drive,  while  the  torque  is  taken 
through  the  springs  and  the  driving  thrust  by  radius  rods. 

The  double-reduction  drive,  like  the  worm  drive,  will  be 
found  on  both  gasoline  and  electric  vehicles,  although  its  use 
seems  to  be  mostly  on  vehicles  of  5,000  Ibs.  capacity  and  under.  . 

The  Internal-gear  Drive. — As  mentioned  above,  the  internal- 
gear  drive  axle  is  really  a  double  reduction,  in  which  two  sets  of 
gears  are  used.  It  is  also  similar  to  the  chain  drive  in  that  a  jack 
shaft  and  dead  rear  axle  are  used.  However,  the  two  units  are 


BRAKE    DRUM 
SPRING  SEAT 


DEAD   AXLE 


1 


PROPELLER  SHAFT 
BRAKE: 


FIG.  123.     Fremont  Mais  Internal  Gear  Axle. 


11 


146    MOTOK  TEUCK  DESIGN  AND  CONSTRUCTION 

bolted  together  and  the  sprockets  and  chains  are  replaced  by  in- 
ternal gears  in  the  brake  drums  and  spur  pinions  on  the  drive 
shafts.  Among  the  users  of  this  type  of  axle  may  be  mentioned 
the  General  Vehicle  Company,  Fremont  Mais,  Mais,  Denby,  Re- 
public, Stewart  and  numerous  others. 

Fig.  123  serves  to  illustrate  the  Fremont-Mais  one-and-a-half- 
ton  axle,  showing  a  dead  rear  axle  of  I-beam  section  with  integral 
spring  seats  and  spindles  carrying  a  bronze  sleeve  and  a  double 
row  ball  bearing  upon  which  the  wheel  is  mounted.  The  jack- 
shaft  unit,  carrying  the  differential,  drive  shafts  and  bevel  driv- 
ing gears,  is  mounted  to  the  rear  of  the  I-beam  axle.  The  hous-- 
ing  of  this  unit  is  riveted  to  the  axle  and  supports  tubes  which 
enclose  the  drive  shafts  and  extend  into  the  brake  spider  to  sup- 
port the  wheel  brakes.  The  drive  shafts  float  in  the  differential 
and  are  supported  inside  the  brake  spider  by  a  double  row  ball 
bearing  next  to  the  spur  driving  pinion.  The  hub  flange  is  made 
large  enough  so  that  the  brake  drum  can  be  riveted  to  it,  while 
inside  the  brake  drum  and  bolted  to  the  hub  is  the  internal  gear. 
The  driving  gear,  with  its  bearing,  is  enclosed  in  a  separate  com- 
partment formed  by  the  brake  drum,  spider  and  hub  and  works 
in  a  bath  of  oil.  One  set  of  brakes  is  located  in  the  wheel  drums 
while  the  other  is  mounted  on  the  bevel  pinion  shaft  and  sup- 
ported from  the  rear  axle.  This  brake  acts  on  both  wheels 
through  the  driving  unit. 

Fig.  124  depicts  the  massive  construction  of  the  Studebaker 
internal  gear  drive  rear  axle  which  possesses  several  unique  fea- 
tures, having  a  dead  rear  axle  on  which  are  mounted  the  bevel 
gear  differential  and  drive  shafts  which  comprise  the  jack  shaft, 
while  the  wheels  are  driven  through  spur  pinions  meshing  with 
internal  spur  gears.  The  whole  mechanism  is  enclosed  and  felt 
packings  are  provided  to  keep  out  dust  and  retain  grease  and  oil 
in  the  various  compartments. 

The  principal  difference  between  this  axle  and  that  above  is 
the  scheme  of  the  brakes.  In  front  of  the  bevel  gears  housing  is 
a  very  wide  brake  drum  on  the  bevel  pinion  shaft.  On  this  drum 
are  the  two  brake  bands  for  foot  and  ratches  hand  brakes,  but  an 
additional  hand  emergency  brake  is  provided  not  ratchet  re- 
tained. It  consists  of  shoes  acting  upon  V-shaped  ribs  running 
around  on  the  outside  of  the  internal  gears  on  the  rear  wheels 
close  to  the  spokes.  It  is  claimed  that  this  construction  relieves 
all  brakes  from  any  danger  of  slipping  due  to  leakage  of  grease 
around  the  rear  wheels  and  yet  provides  a  brake  acting  upon  the 


THE  FINAL  DEIVE 


147 


FIG.  124.     Sttfdebaker  Internal  Gear  Drive  Axle. 


FIG.  125.     Russell   Internal   Gear  Axle. 


148    MOTOE  TEUCK  DESIGN  AND  CONSTEUCTION 


rear  wheels  themselves  in  case  any  breakage  should  put  the  regu- 
lar brakes  out  of  commission. 

With  this  axle,  triangular  channel  shaped  pressed  members 
which  are  bolted  to  the  brake  spiders  and  hinged  to  a  heavy 

cross  member  take  up  the 
thrust  and  torque  loads. 

The  G.  V.  Mercedes 
gasoline  trucks  are  also  in- 
ternal gear  driven.  While 
they  are  similar  in  some 
respects  to  the  Studebaker 
construction,  the  axle  is 
equipped  with  only  one 
set  of  brakes,  while  the 
other  brake  is  mounted  in 
back  of  the  transmission. 
They  also  use  the  trian- 
gular pressed  steel  mem- 
bers for  taking  torque  and 
thrust  loads,  but.  have  a 
cross  member  located  di- 
rectly in  front  of  the  jack 
shaft  and  bolted  to  it,  and 
the  triangular  members. 

The  Eussell  internal 
gear-drive  axle  illustrated 
in  Fig.  125  has  a  forged 
steel  dead  axle  of  round 
section  with  spring  seats 
keyed  to  it  so  the  torque 
and  thrust  can  be  taken  on 
the  springs.  The  axle  is 
similar  to  those  mentioned 
above. 

There  is  one  feature 
about  the  internal  gear  in 
that  it  employs  two  reduc- 
tions as  mentioned  above 
and  is  similar  to  the  chain 
drive.  The  first  reduction  is  through  bevel  gears  and  is  such  that 
a  low  torque  is  transmitted  by  the  rapidly  revolving  drive  shafts, 


THE  FINAL  DRIVE 


149 


which  permits  a  light  structure  for  the  driving  unit.  The  next 
reduction,  of  course,  is  near  the  wheels  and  supported  directly 
by  them.  The  reduction  in  the  wheels  is  such  as  to  provide  a  high 
torque  direct  to  the  wheels.  By  making  the  jack  shaft  a  high- 
speed unit,  considerable  weight  can  be  saved.  However,  it  has 
a  greater  unsprung  weight  than  the  chain  drive. 

The  Torbensen  axle  shown  in  Fig.  126  is  also  of  the  internal 
gear  type.  The  dead  axle  is  a  one-piece  drop  forging  of  I-beam 
section,  with  chrome  vanadium  spindles  and  fixed  spring  seats. 
The  cylindrical  end  of  the  dead  axle  is  of  large  diameter,  and  ex- 
tends nearly  to  the  center  line  of  the  spokes,  so  that  the  bending 
moment  of  the  spindle  is  reduced  to  a  minimum.  All  members  of 
the  jack  shaft  are  enclosed,  affording  cleanliness,  efficient  lubrica- 
tion and  quiet  working. 


FIG.  127.     Clark   Internal    Gear   Driven  Eear   Axle. 

The  Clark  axle  (Fig.  127)  is  another  type  of  internal  gear- 
drive  axle,  with  a  load  carrying  member  of  round  section.  A 
feature  of  this  axle  is  that  all  parts  are  identical,  there  being  no 
rights  and  lefts.  The  driving,  unit  is  located  in  front  of  the  load 
carrying  member  and  instead  of  supporting  at  the  center,  the 
driving  unit  is  supported  at  each  end  from  the  integral  spring 
seats  and  brake  spider.  The  differential  and  drive  shafts  are 
supported  on  Hyatt  roller  bearings  and  ball  thrust  bearings, 
while  the  wheels  are  supported  on  double  row  ball  bearings. 

The  White  3-  and  5-ton  trucks  are  equipped  with  a  combina- 
tion double  reduction  and  internal  gear-drive  axle.  This  axle 
(Fig.  128),  called  a  double-reduction  drive,  but  in  reality  an  in- 
ternal gear  drive,  has  a  floating  rear  axle  concentric  with  the 


150    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

axle  housing.  The  power  from  the  propeller  shaft  is  trans- 
mitted to  the  usual  bevel  gear  set  and  differential  which  in  turn 
drive  the  axle  shafts.  These  shafts  have  spur  pinions  mounted 


FIG.  128.     New  Type  of  Double  Eeduction  and  Internal  Gear  Drive  Axle 
used  on  White  3  and  4  Ton  Trucks. 


inside  the  hub  case  which  mesh  with  another  spur  pinion  which 
in  turn  meshes  with  the  internal  gear  bolted  to  the  hub  of  the 
wheel.  By  this  method  of  applying  the  power  to  the  wheel,  a 


FIG.  129.     Fierce-Arrow  Worm  Drive  Axle. 

second  reduction  is  obtained  between  the  three  gears  in  the  hub 
case  very  much  like  the  reduction  which  takes  place  between  the 
sprocket  wheels  of  a  chain  drive. 


THE  FINAL  DEIVE 


151 


The  Worm  Drive. — In  spite  of  bitter  opposition,  worm  drive 
has  made  great  strides  during  the  past  year,  quite  a  number  of 
makers  having  added  worm-driven  models  to  their  line,  good 
axles  of  this  type  being  obtainable.  Several  of  the  older  com- 
panies are  building  their  own  axle,  amongst  these  being  the 
Pierce,  Packard  and  Locomobile  companies,  the  former  adding  a 
two-ton  model,  while  the  latter  have  recently  announced  three- 
and  four-ton  models. 

Fig.  129  will  serve  to  illustrate  the  Pierce  axle  which  is  of  the 
full-floating  type,  with  the  worm  mounted  above  the  wheel.  The 
worm,  worm  wheel  and  spur  gear  differential  are  mounted  on  ball 
bearings  and  assembled  as  a  unit  with  the  cover.  This  construc- 
tion permits  the  removal  of  the  entire  unit  without  disturbing 
the  balance  of  the  axle,  as  shown  in  the  illustration.  The  hous- 
ing is  a  heavy  steel  casting  reinforced  by  tubes  which  carry  the 
wheel  bearing  and  extend  beyond  the  spring  seats.  The  emer- 
gency brakes  are  mounted  in  the  rear  wheels  and  the  service  brake 
is  located  back  of  the  transmission.  Thrust  is  taken  on  radius 
rods  and  the  torque  load  on  a  heavy  torque  arm.  The  road  wheel 
is  driven  through  a  squared  shaft  and  driving  flange  bolted  to  the 
hub. 

The  worm-drive  axle  recently  introduced  by  the  Locomobile 
Company  is  illustrated  in  Fig.  130,  and  is  also  of  the  full-floating 
type.  However,  it  differs  from  the  above  in  that  a  bevel-gear 


DUAL  TIRE 


THRUST  BEARING 


BRAKEDRUM 


FTG.  130.     Riker  Worm  Drive  Axle. 


differential  is  used,  while  the  housing  is  divided  into  three  parts, 
consisting  of  a  center  housing  and  two  ends  which  are  bolted 
together.  Reinforcing  tubes  are  also  used,  which  carry  the 


152    MOTOE  TRUCK  DESIGN  AND  CONSTRUCTION 

wheel  bearings  and  extend  to  points  just  outside  the  differential 
bearings.  The  ends  of  these  carry  a  series  of  packing  washers 
to  prevent  the  oil  working  out  onto  the  brakes.  The  outer  ends 
of  the  housing  have  spherical  bearings  for  the  radius  rods,  while 
the  spring  seats  pivot  on  bronze  bushings.  The  spring  is  mounted 
outside  the  frame  while  the  radius  rods  are  placed  directly  under 
the  side  frame  members.  The  worm  is  mounted  above  the  wheel 
and,  together  with  the  differential  and  bearings,  forms  a  unit 
with  the  cover.  A  heavy  truss  rod  is  anchored  to  the  housing 


FIG.  131.     Timken  Worm  Drive  Axle. 

inside  the  brake  drum  and  provided  with  a  turnbuckle  for  adjust- 
ment. The  wheels  are  mounted  on  Timken  heavy  roller  bear- 
ings, while  the  driving  unit  is  mounted  on  ball  bearings  and  pro- 
vided with  suitable  thrust  bearings.  The  drive  shafts  are  of  the 
ten-spline  type,  and  drive  the  wheels  through  flanges  bolted  to 
the  wheel  hubs.  Attention  might  be  called  to  the  method  of  re- 
ducing the  weight,  by  lightening  the  reinforcing  tube.  The  inner 
wall  of  this  tube  tapers  from  the  end  to  the  center  of  spring 
seat,  from  this  point  to  just  inside  the  inner- wheel  bearing  where 
the  greatest  load  comes. 

The  Timken  David  Brown  axle  used  in  a  number  of  commer- 
cial cars  is  depicted  in  Fig.  131,  being  similar  in  construction  to 
those  described  above,  with  the  worm,  worm  wTheel,  differential 
and  their  bearings  assembled  into  a  unit  with  the  cover.  How- 
ever, in  this  axle  the  well-known  Timken  bearings  are  used 
throughout,  and,  owing  to  their  ability  to  carry  thrust  loads,  it 
is  claimed  no  thrust  bearings  are  necessary.  To  the  writer's 
knowledge  this  company  is  the  only  one  resorting  to  roller  bear- 
ings for  mounting  of  the  worm.  The  flange  for  driving  the 
wheels  is  forged  integral  with  the  drive  shaft,  while  the  general 
construction  is  along  conventional  lines. 


THE  FINAL  DRIVE 


153 


Another  worm-drive  axle  used  by  several  commercial  car 
builders  is  the  Sheldon  axle  (Fig.  132).  It  is  also  constructed 
along  conventional  lines,  having  the  differential  and  worm  gear 
a  unit.  However,  it  is  of  the  semi-floating  type,  and  the  housing, 
which  is  cast  in  one  piece,  is  so  arranged  that  either  over  or 
underslung  springs  may  be  used.  As  the  axle  is  of  the  semi- 


FIG.  132.     Sheldon  Worm  Drive  Axle   Semi-Floating  Type. 

floating  type,  the  housing  is  made  of  liberal  proportion  and  the 
weight  is  carried  on  the  drive  shaft,  while  a  ball  bearing  is 
mounted  inside  of  the  wheel  which  is  attached  and  driven  by 
means  of  a  long  taper 'and  key.  This  is  clearly  shown  in  the  illus- 
trations. The  features  of  semi-floating  axles  can  perhaps  be  best 
described  by  comparing  with  the  full-floating  and  three-quarter- 
floating  types. 


FIG.  133.     Phantom  View  of  Packard  Worm  Drive  Axle. 


154    MOTOK  TRUCK  DESIGN  AND  CONSTRUCTION 

The  Packard  worm-drive  axle  (Fig.  133)  also  has  a  three- 
piece  housing,  with  the  differential  and  driving  unit  mounted  in  a 
unit  with  the  cover.  The  differential  is  spur-gear  type,  and  the 
entire  driving  unit  is  mounted  on  ball  bearings  and  provided  with 
suitable  thrust  bearings.  As  in  the  construction  described  above, 
the  worm  is  mounted  above  the  wheel.  The  housing  is  massive 
steel  construction,  well  ribbed  to  provide  maximum  strength. 
The  entire  construction  is  arranged  for  straight-line  drive  from 
the  transmission  through  two  universals,  while  the  thrust  is 
taken  by  radius  rods  and  the  torque  by  a  heavy  torque  arm. 

Rear  Axle  Types. — Shaft-driven  commercial  car  axles  may 
be  classified  according  to  the  arrangement  of  the  wheel  bearings. 
If  the  end  of  the  drive  shaft  next  to  the  wheel  has  a  bearing 
directly  upon  it,  the  axle  is  then  classed  as  semi-floating  type. 
This  type  of  axles  possesses  some  advantages  in  cost  of  manu- 
facture and  simplicity,  and  is  the  lightest  axle  for  its  strength. 

The  great  strains  imposed  upon  the  bearings  and  housing  of 
the  full-floating  type  in  skidding  against  obstructions  are  much 
less  in  the  semi-floating  type,  because  of 'the  greater  distance 
between  bearings.  However,  there  is  much  difference  of  opinion 
as  to  the  relative  advantages  of  the  various  types  of  axles. 

In  the  semi-floating  axle,  the  drive  shaft  carries  the  weight 
of  the  vehicle  and  must  also  resist  torsional  strain. 

In  order  to  make  an  axle  in  which  only  torsional  driving 
strains  are  imposed  upon  the  drive  shaft — thus  approximating 
some  advantages  of  the  dead  rear  axle — a  construction  is  used 
wherein  each  wheel  is  mounted  outside  the  axle  housing,  and  the 
drive  is  taken  through  a  central  shaft  connected  to  the  hub  by 
either  a  jaw  clutch  or  flange  bolted  to  the  hub.  This  is  known  as 
the  full-floating  type  of  axle.  It  has  the  advantage  of  having 
the  axle  shaft  free  from  all  lateral  strains,  thus  greatly  reducing 
the  danger  of  breakage  and  of  bending,  the  latter  causing  the 
wheel  to  wabble.  Even  if  the  shaft  is  broken,  the  wheel  is  still 
securely  mounted  on  the  axle  housing,  so  that  the  axle  does  not 
drop  to  the  ground.  The  construction  is  such  that  the  drive 
shafts  can  be  withdrawn  and  even  the  differential  dismounted 
without  removing  the  wheels  from  the  axle,  or  the  axle  from  the 
car. 

The  jaw  clutch  for  driving  the  wheel  has  the  advantage  of 
being  more  easily  withdrawn  from  the  axle  and  affords  more 
freedom  to  allow  for  misaligning  parts,  while  the  flange  drive 


THE  FINAL  DEIVE  155 

removes  all  chances  of  noise  sometimes  made  by  jaw  clutches, 
and  is  claimed  to  be  sligthly  less  expensive  to  construct. 

The  three-quarter-floating  axle  is  a  compromise  between  the 
semi-floating  and  full-floating  types.  It  has  the  wheel  mounted 
on  a  single  bearing  outside  the  axle  housing  on  a  reinforcing 
tube,  and  kept  in  alignment  by  being  rigidly  attached  to  the 
driving  shaft  by  either  a  key,  as  in  the  semi-floating  type,  or  a 
flanged  connection  as  in  one  style  of  full-floating  axle.  Accord- 
ing to  the  type  of  bearing  employed  at  the  wheel,  the  axle  shaft 
is  held  in  place  either  by  the  wheel  bearing  or  by  some  sort  of  a 
lock  near  the  differential. 

As  in  most  compromises,  this  type  possesses  some  of  the  ad- 
vantages of  each  of  the  others.  No  dead  load  is  placed  on  the 
axle  shaft,  but  the  skidding  strains  are  little,  if  any,  different  on 
the  bearings  and  shafts  than  with  the  semi-floating  type.  As  in 
the  semi-floating  axle,  any  type  of  bearing  can  be  used,  and  the 
weight  may  be  less  than  the  full-floating  axle.  When  the  wheel 
bearings  are  of  a  type  suitable  to  take  end  thrust,  they  are  usually 
so  mounted  as  to  hold  the  wheel  in  place  on  the  axle  end,  and  the 
shaft  is  connected  by  a  flange.  The  shaft  can  then  be  removed 
without  disturbing  the  wheel. 

Worm  and  bevel-gear  axles  are  similar  to  pleasure  car  axles, 
and  various  parts  of  the  other  two  types  are  also  similar;  how- 
ever, while  they  are  similar,  their  proportions  are  materially  in- 
creased to  withstand  vibration. 

Method  of  Providing  for  Torsion  and  Propulsion  in  Shaft- 
driven  Commercial  Cars. — At  the  present  writing  there  seem  to  be 
about  five  methods  of  providing  for  torque  and  thrust  loads  on 
shaft-driven  axles,  as  follows:  (1)  torque  and  thrust  through  the 
vehicle  springs;  (2)  torque  and  thrust  through  triangular  struc- 
ture attached  to  a  rigid  cross  member;  (3)  torque  on  springs, 
thrust  on  radius  rods;  (4)  separate  torque  and  radius  rod  mem- 
bers; (5)  torque  tube  surrounding  drive  shaft  and  anchored  to 
the  frame  by  a  large  yoke  and  triangular  radius  rods  anchored  to 
the  torque  tube. 

In  a  shaft-driven  axle  there  are  two  separate  torsional  forces. 
There  is  first,  the  primary  torque  of  the  drive  shaft,  and  the  sec- 
ondary torque  of  the  axle  itself.  The  inertia  of  the  axle  causes 
the  shaft  to  react  upon  the  gear  set  support  in  a  tendency  to 
whirl  them  instead  of  itself  turning,  and  the  inertia  of  the  wheels 
on  the  road  tends  to  cause  the  axle  to  whirl,  instead  of  the  wheels 


156    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

revolving.  Owing  to  the  reduction  afforded  by  the  gear  set  on 
the  lower  gears,  there  is  a  certain  amount  of  drive-shaft  torsion, 
even  on  a  heavy  vehicle.  It  is  no  greater,  however,  the  motor 
being  of  the  same  power  as  in  a  passenger  vehicle,  as  a  rule,  and, 
as  in  the  latter,  it  can  be  transmitted  directly  to  the  frame,  the 
springs  being  the  medium  relied  upon  to  absorb  it. 

The  axle  torque  offers  the  greatest  problem.  In  some  vehicles 
the  springs  or  the  ordinary  form  of  torque  arm  supported  from 
the  frame  have  proven  successful,  while  in  other  cases  torsion  is 
provided  for  by  connecting  the  sub-frame,  upon  which  the  com- 
plete power  plant  and  transmission  system  are  mounted,  to  the 
rear  axle  at  one  point  and  to  the  forward  part  of  the  frame  on 
two  points.  Propulsion  may  be  through  the  swinging  sub-frame, 
torque  tube,  springs  or  radius  rods.  When  radius  rods  are  used, 
the  springs  are  shackled  at  both  ends,  and  when  the  thrust  is 
taken  through  the  springs  the  front  end  is  rigidly  attached  to  the 
frame  and  the  rear  end  is  shackled. 

There  seems  to  be  a  very  wide  difference  of  opinion  as  to  the 
relative  merits  of  .the  various  methods,  and  examples  of  each 
type  may  be  found  with  either  type  of  axle.  The  method  of  tak- 
ing stresses  on  the  springs,  which  is  termed  the  Hotchkiss  drive, 
has  been  quite  popular  on  the  lighter  vehicles  and  at  the  present 
there  seems  to  be  a  general  tendency  to  apply  it  to  the  heavier 
vehicles  also.  The  separate  torque  and  radius  rod  construction  is 
also  used  on  a  number  of  heavy  worm-driven  vehicles. 


TT 


"TT 


FIG.  134.     Arrangement  of  Springs  for  Taking-  Torsion  and  Thrust.     This 
is  called  the  Hotchkiss  Drive. 

The  internal  gear-driven  vehicles  are  divided  between  Hotch- 
kiss drive  and  triangular  members  anchored  to  the  frame  cross 
member  for  taking  up  these  stresses.  The  double  reduction  seems 
to  favor  the  worm  practice,  as  both  of  these  methods  are  found, 
while  the  bevel  drive  seems  to  favor  pleasure  car  methods. 


THE  FINAL  DRIVE 


157 


Fig.  134  depicts  the  spring  mounting  for  Hotchkiss  drive,  in 
which  both  torque  and  thrust  are  taken  by  the  springs.  The  front 
ends  of  the  springs  are  rigidly  mounted  in  a  heavy  bracket  at- 
tached to  the  frame,  while  the  rear  ends  are  shackled  in  the  usual 
manner.  The  springs  must  be  made  with  as  little  camber  as  pos- 
sible, that  is,  the  spring  should  be  nearly  flat  under  load,  so  that 
the  driving  effort  is  applied  lengthwise  of  the  top  leaf,  the  direc- 
tion of  the  effort  lying  within  the  metal  instead  of  across  a  chord 
of  the  arc  outside  it. 


FIG.  135.     Diamond  T-Spring  Anchorage. 

Springs  for  Hotchkiss  drive  must  be  especially  designed  to 
take  these  stresses  and  require  numerous  rebound  clips. 

Some  excellent  features  have  been  developed  lately  which 
show  how  the  problems  connected  with  this  type  of  drive  have 
been  solved.  Nickel  steel  U-boats  are  used  by  many,  while  others 
are  providing  rigid  anchoring  of  the  springs  to  axle  in  various 
ways.  As  flat  springs  must  be  used,  this  necessitates  a  rigid 
anchorage  to  prevent  the  pressure  blocks  from  creeping. 

On  the  Diamond  T-trucks  particularly  rigid  anchoring  of  the 
spring  to  the  axle  is  used.  This  is  shown  in  Fig.  135,  and  con- 
sists of  a  special  casting  which  is  U-shaped  and  snugly  fits  the 
spring.  On  top  of  this  casting  is  a  special  block,  which  is  re- 
cessed to  take  an  upward  arch  in  the  center  of  the  top  leaf  of  the 
spring.  On  the  vertical  sides  of  the  U-casting  are  heavy  shoulders 


158    MOTOK  TRUCK  DESIGN  AND  CONSTRUCTION 


FIG.  136.    Torque  taken  on  Springs.    Driving  Thrust  taken  on  Radius  Rods. 


FIG.  137.     Triangular  Torque  and  Radius  Rods  Applied  to  Internal  Gear- 
Drive  Axle. 


THE  FINAL  DRIVE 


159 


bearing  against  the  clips  or  U-bolts  and  so  preventing  displace- 
ment of  these.  This  feature  of  keeping  the  clips  at  right  angles 
to  the  spring  leaves  is  an  essential  of  this  type  of  drive.  The 
Winther  trucks  are  provided  with  a  similar  arrangement,  while 
on  the  Military  class  B  trucks  the  spring  plates  are  provided 
with  spherical  depressions  which  lock  the  spring  plates  and  pre- 
vent creeping. 

Those  makers  who  do  not  provide  any  special,  anchorage  give 
special  attention  to  have  anchorage  as  rigid  as  possible  with  the 
use  of  a  specially  flat  spring  with  heavy  upper  leaves.  Spring 


FIG.  138.     Separate  Torque  and  Baclius  Rods. 

seats  are  usually  machined  to  the  center  of  the  spring  and  all 
points  of  contact  are  carefully  white-leaded  so  that  both  air  and 
water  are  kept  out  of  the  joints. 

On  the  new  G.  M.  C.  worm-driver  trucks,  the  springs  are 
shackled  at  both  ends  and  take  the  torque  load,  while  radius  rods 
are  used  to  take  the  driving  thrust  as  shown  in  Fig.  136. 

Fig.  137  illustrates  the  method  of  taking  these  stresses  on 
tubular  rods  forming  a  triangular  construction  with  the  rear 
axle.  The  tubes  are  rigidly  attached  to  the  brake  supports  at  the 
rear,  and  form  a  large  ball  at  the  forward  end,  which  is  mounted 
in  a  spherical  bearing  on  the  frame  cross  member,  directly  over 
or  under  the  universal  joint.  This  construction  will  be  found  on 
several  internal  gear  models. 


160    MOTOE  TEUCK  DESIGN  AND  CONSTEUCTION 

The  dotted  lines  in  this  illustration  show  another  type  of 
triangular  torque  and  radius  rods.  However,  each  rod  is  hinged 
separately  on  each  side  of  the  universal  joint  to  the  frame  cross 
member.  This  construction  is  used  on  the  Studebaker  and  G.Y. 
internal  gear-driven  vehicles  and  the  Flint  double  reduction  drive 
and  others. 

Separate  torque  and  radius  rods  are  used  on  the  Pie'rce,  Loco- 
mobile, Packard  and  other  dorm-driven  models,  and  the  Menomi- 
nee  double-reduction  drive,  the  latter  being  shown  in  Fig.  138. 
The  torque  rod  is  a  pressed-steel  channel-shaped  member,  having 
a  ball  end,  which  is  mounted  between  springs  in  a  bracket  hinged 
to  the  axle  and  frame  side  rails. 


FIG.  139.     Manly  Method  of  Taking  Drive  and  Torsional  Strains. 

On  the  Manly  trucks,  the  radius  rods  (Fig.  139)  are  of  pecul- 
iar construction  and  in  addition  to  taking  the  torque  and  driving 
strains  also  maintain  the  axle  in  correct  relation  to  the  drive 
shaft,  thus  releasing  the  rear  universal  joint  of  any  irregularity. 
Connection  from  the  frame  to  the  axle  is  made  by  means  of  a  pair 
of  rods  on  each  side,  the  rods  of  one  pair  being  placed  above  the 
other  and  pivoted  at  both  the  axle  and  frame  ends.  The  driving 
force  passes  through  both  rods,  being  taken  from  a  point  under 
the  springs  and  in  line  with  the  axle  center  to  a  heavy  steel 
bracket  on  the  frame.  The  tendency  for  the  axle  housing  to 
rotate,  which  it  is  a  natural  result  of  the  reaction  of  the  wheels  in 
driving,  is  resisted  by  these  pairs  of  rods.  This  torque  reaction 
compresses  one  rod  and  pulls  on  the  other  and  because  of  their 
pivoted  mounting  it  is  impossible  to  place  a  binding  strain  on 
either  rod.  The  upper  and  lower  rods  on  each  side  of  the  chassis 
are  not  quite  parallel  with  each  other,  their  distances  apart  front 
and  rear,  being  so  proportioned  that  the  rear  axle  itself  is  caused 
to  move  in  a  curve  that  would  result  from  an  ideal  condition  of 
having  radius  rods  as  long  as  the  propeller  shaft  tube  and  having 
their  front  pivots  in  line  with  the  front  universal.  Deflection 
of  the  rear  universal  is  thus  entirely  done  away  with. 


THE  FINAL  DRIVE  161 

With  bevel-drive  axles  there  are  several  methods  in  use,  which 
follow  pleasure-car  practice  closely.  The  torque  tube  may  either 
surround  the  drive  shaft  and  the  drive  be  taken  through  the 
spring  and  the  radius  rod,  as  in  the  Commerce,  Vim  and  others, 
or  the  torque  and  thrust  may  be  taken  through  a  torque  tube  and 
radius  rod  hinged  to  the  cross  member,  as  advocated  by  the 
G.M.C.  1,500-lb.  delivery  car,  which  is  illustrated  in  Fig.  119. 

There  are  various  arguments  which  can  be  advanced  for  either 
of  these  constructions,  while  each  type  seems  to  have  its  share  of 
support  amongst  the  manufacturers.  From  the  writer's  ob- 
servations it  seems  to  be  the  general  tendency  to  let  the  springs 
perform  these  functions  in  the  lighter  vehicles,  and  to  use  radius 
and  torque  rods  and  combinations  of  these  on  the  heavier  models. 


12 


CHAPTEK  XI 

FEONT-  AND  FOUR-WHEEL  DRIVES 

IN  the  foregoing  chapters  on  the  final  drive,  we  considered 
all  types  of  final  rear  wheel  drives.  There  are  also  a  number  of 
commercial  cars,  in  which  the  final  drive  is  through  the  front 
wheels,  and  others  in  which  it  is  through  all  four  wheels.  Both 
of  these  types  have  gained  considerably  in  popularity  of  late. 
This  is  possibly  due,  to  some  extent,  to  the '  demands  of  the 
various  war  departments,  for  motor-driven  vehicles,  which  can 
propel  themselves  to  any  point  where  mules  can  pull  a  wagon. 

This  same  ability  is  also  of  great  importance  in  many  other 
classes  of  service,  where  departure  from  the  road  surface  is  some- 
times necessary.  It  is  especially  of  importance  to  coal  dealers, 
who  are  generally  called  on  to  make  deliveries  in  narrow  alleys; 
excavating  contractors,  who  must  haul  material  in  and  out  of 
excavations,  building  supply  concerns,  handling  such  as  lumber, 
gravel,  brick,  etc.,  over  unpaved  roads  and  sometimes  across 
swampy  land  to  deliver  the  material  to  the  building  site.  There 
are  also  other  cases  to  which  the  four-wheel  drive  is  adaptable. 

There  is  also  a  variety  of  cases  in  which  extremely  low  bodies 
are  necessary,  as  in  hauling  long  structural  girders,  timbers  and 
heavy  stone.  On  the  other  hand,  there  are  such  problems  as 
handling  light  paper,  boxed  paper  and  tin  cans  and  tubes  and 
other  articles  which  present  a  very  bulky  load.  For  these  pur- 
poses, the  front-wheel  drive  lends  itself  to  best  advantage,  while 
it  is  also  of  considerable  advantage  for  fire  apparatus,  etc.,  where 
it  is  desired  to  retain  the  vehicles  used  with  the  horse  equipment. 

Foreign  manufacturers  were  the  first  to  experiment  with  these 
types  of  vehicles  and  have  perhaps  led  the  way;  however,  there 
are  a  number  of  companies  in  America,  which  are  prepared  to 
manufacture  these  types  of  vehicles.  As  the  front-wheel  and 
four-wheel  drives  are  closely  related,  and  practically  involve  the 
same  mechanical  problem  in  driving  and  steering,  they  will  be 
considered  together. 

Four  Methods  of  Drive. — In  comparing  the  various  designs 
we  find  four  methods  of  driving  and  two  methods  of  steering. 
In  the  first  construction,  the  whole  axle  pivots  about  its  center 

162 


FKONT-  AND  FOUR-WHEEL  DRIVES 


163 


and  the  wheels  are  driven,  as  in  the  ordinary  dead  or  live  rear 
axle.  This  construction  is  mostly  used  with  front-drive  units, 
that  is,  in  vehicles  propelled  through  the  front  wheels  only.  In 
the  second  type,  the  axles  have  steering  knuckles,  as  in  the  con- 
ventional type,  but  the  flexibility  is  obtained  through  universal 
joints  or  chains  driving  the  wheels  through  internal  gearing. 
In  the  third  type,  the  wheels  are  driven  through  bevel  gears 
mounted  inside  the  wheel  and  on  the  steering  knuckles,  another 
pair  of  bevel  gears  mounted  on  the  steering  knuckles  driving  the 
wheels,  through  shafts  extending  from  the  central  pair  of  gears 
in  the  axle  housing.  These  three  are  termed  mechanical  drives; 
while  the  fourth  construction  is  a  non-mechanical  drive,  electric 
motors  being  mounted  in  the  wheels  and  driving  direct  through 
reduction  gearing. 

The  front-wheel  drives,  in  some  cases,  are  so  constructed  that 
this  forms  the  power  unit,  which  may  be  attached  to  any  type  of 
vehicle  the  user  may  desire,  while  a  rear  frame  construction,  upon 
which  any  type  of  body  can  be  mounted,  may  also  be  provided. 
With  the  latter,  the  rear  wheels  may  be  shod  with  steel  or  rubber 
tires  as  desired.  The  Devon,  Pull-More,  and  Meyers  may  be  men- 
tioned as  examples  of  this  type. 

Whole  Front  Unit  Pivoting  Chain  Drive. — Referring  to  Fig. 
140,  illustrating  the  Devon  Tractor  Trailer,  the  engine  is  mounted 


u-e 


FIG.  140.     Plan  View  of  the  Devon  Tractor. 


164    MOTOE  TEUCK  DESIGN  AND  CONSTEUCTION 

in  front  of  the  axle  and  placed  lengthwise.  It  is  located  toward 
the  left  side  and  enclosed  by  a  metal  hood.  At  the  rear  of  this 
hood  is  the  vertical  steering  column,  and  back  of  this,  a  metal 
seat.  The  power  from  the  engine  is  transmitted  to  the  clutch 
and  transmission  at  the  rear,  the  transmission  being  a  unit  with 
a  jackshaft,  as  in  the  ordinary  chain-driven  truck.  The  front 
axle  is  similar  to  the  ordinary  dead  rear  axle,  and  carries  a  set 
of  brakes  and  sprockets.  From  the  jackshaft,  the  power  is  trans- 
mitted to  the  front  wheels  through  chains,  which  are  enclosed. 
In  steering,  the  entire  unit  is  turned  bodily  by  means  of  the  steer- 
ing wheel,  through  bevel  gears,  rotates  a  worm,  engaging  the  cir- 


FIG.  141.     The  Meyers  Tractor. 

cumference  of  a  large  worm  wheel  attached  to  the  forward  part 
of  the  main  frame  and  concentric  with  the  pivot.  This  worm  is 
mounted  on  a  splined  shaft,  between  heavy  coil  springs  to  absorb 
the  road  shocks. 

The  Pull-More  front  drive  is  similar  to  the  above;  but  has  a 
power  steering  device  operated  by  the  engine,  this  steering  device 
working  through  a  sprocket  on  the  crankshaft,  which,  by  means 
of  a  chain,  drives  a  countershaft,  located  in  the  lower  half  of  the 
crank  case.  This  countershaft  operates  the  arm  of  the  steering 
reach,  which  is  a  part  of  the  king  bolt.  This  king  bolt  is  located 
midway  between  the  front  wheels,  and  forms  the  axis  upon 
which  the  entire  front  unit  revolves.  Differentials  are  provided 
to  permit  right-and-left-hand  steering.  An  ordinary  steering 
post  and  wheel  is  used  to  operate  the  power  steering  device. 


FKONT-  AND  FOUE-WHEEL  DKIVES 


165 


The  Meyers  front  drive  (Fig.  141)  is  similar  to  the  above 
types,  in  that  the  engine  is  placed  forward  of  the  front  axle. 
The  power  of  the  motor  is  transmitted  from  the  jackshaft,  through 


FIG.  142.     Side  and  Plan  View  of  Walter  Transmission  and  Front-Wheel 

Drive. 

side   chains,   to    a    shock   absorbing   bracket,    carrying    another 
sprocket  attached  to  a  short  shaft,  on  the  opposite  end  of  which 


166    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

is  a  small  gear,  meshing  with  a  large  internal  gear,  bolted  to  the 
spokes  of  the  wheels.  The  main  frame  is  mounted  upon  semi- 
elleptic  springs.  The  upper  frame,  which  forms  the  pivoting 
member,  has  a  detachable  castor-like  wheel  and  as  the  weight  is 
to  the  rear  of  the  unit,  it  is  perfectly  stable  and  can  be  driven 
from  place  to  place.  The  vehicle  is  steered  by  means  of  a  circular 
rack  and  pinion,  upon  a  fifth  wheel.  The  shock  of  starting  is 
eliminated  by  a  patented  arrangement  on  the  driving  pinion. 
This  pinion  is  mounted  on  an  arm  pivoted  by  the  axle  and  is 
free  to  roll  in  the  internal  gear  to  a  slight  extent,  its  forward 
motion  being  limited  by  a  positive  stop  and  its  rearward  motion 
by  the  rod  and  spring  shown. 

Gear  Drive. — In  the  types  described  above,  the  power  is  trans- 
mitted to  the  wheel  by  means  of  roller  chains.  In  the  Walter 
truck  the  power-  is  transmitted  by  shafts  and  internal  gears,  along 
lines  similar  to  the  Latil  front-drive  trucks,  built  in  France.  The 
transmission  of  the  Walter  is  mounted  with  the  engine,  to  form 
a  unit  power  plant,  which  is  so  located  that  the  flywheel  is  just 
in  front  of  the  front  axle,  the  entire  engine  overhanging  the  axle. 
From  the  sectional  view  of  the  transmission  (Fig.  142),  it  will  be 
noted  that  the  differential  and  bevel  driving  gears  are  mounted 
at  the  front  end  of  the  secondary  shaft,  which  is  placed  above 
the  main  shaft.  From  the  differential,  extends  two  universally 
jointed  shafts  to  spur  gear  pinions  on  the  steering  knuckles, 
which  mesh  with  internal  gears  bolted  to  the  front  wheels.  There 
is  no  mechanism  whatever  back  of  the  driver's  seat,  and  the  con- 
struction is  very  compact. 

Four-wheel  Drive. — The  layout  is  such  that  the  front-drive 
unit  does  not  have  to  be  altered  or  changed  in  any  way  on  vehi- 
cles, which  drive  the  rear  wheels  also,  the  forward  unit  of  the 
front  drive  being  identical  with  the  front  unit  of  the  four-wheel 
driven  vehicle.  The  secondary  shaft  of  the  transmission  is  ex- 
tended back  to  another  differential  and  bevel  driving  unit, 
mounted  on  a  frame  directly  over  the  rear  axle.  This  unit  also 
has  universal  jointed  shafts,  extending  to  the  rear  steering 
knuckles  and  carrying  spur  pinions,  which  mesh  with  internal 
gears  bolted  to  the  rear  wheels. 

The  rear  axle  is  also  used  for  steering  in  the  four-wheel  drive, 
but  not  in  the  front  drive. 

The  conventional  type  of  worm  and  gear-steering  column  is 
used,  with  a  longitudinal  cross-shaft,  having  a  universal  joint  at 


FEONT-  AND  FOUR-WHEEL  DRIVES 


167 


its  forward:  end.  The  rear  end  of  this  shaft  carries  a  steering 
arm,  which  is  connected  with  the  usual  linkage  to  the  rear  wheels, 
as  shown  in  Fig.  143. 


FIG.  143.     Plan  of  the  Walter-Four- Wheel  Drive  Chassis. 

The  Nash  Quad  and  Duplex  four-wheel  drive  trucks  are  also 
driven  by  means  of  internal  gears  and  universal- jointed  shafts. 
The  wheel  construction  of  the  Nash  Quad  is  shown  in  Fig.  144. 
The  propeller  shafts  are 

driven  from  the  secondary  I  rZ IL, 

shaft  of  the   transmission.  1 1  A^TTiHffl        _r~~  "ZL 

The  cross-shafts,  which 
drive  the  wheels,  are  lo- 
cated above  the  axle,  while 
the  axle  carries  the  weight 
only  and  has  the  driving 
gear  and  differential  unit 
bolted  to  it.  The  driving 
pinion  meshes  writh  an  in- 
ternal gear,  mounted  in  the 
wheel.  The  wheels  are  cast 
steel  with  integral  rim, 
hubs  and  brake  drums.  The 
driving  pinion  is  located 
above  the  steering  knuckle  and  driven  through  a  universal  joint, 
the  center  of  which  is  directly  in  line  with  the  pivot  center  of  the 
knuckle. 


FIG.  144. 


Nash  Quad  Method  of  Driving 
Four  Wheels. 


168    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

Combined  Chain  and  Shaft  Drive. — The  Duplex  is  also  driven 
by  means  of  internal  gears  in  the  wheels  and  universal  joints 
mounted  directly  over  the  steering  knuckles,  and  with  drive 
shafts  above  the  springs.  However,  the  method  of  transmitting 
the  power  to  the  wheels  is  somewhat  different  from  that  described 
above.  The  transmission  is  of  conventional  design  and  built  in  a 
unit  with'the  engine.  Power  is  transmitted  by  shaft  to  a  chain 
case,  attached  to  the  frame  at  approximately  its  center.  This  oil- 


FIG.  145.     Duplex   Four-Wheel   Drive   Chain   Case. 

tight  chain  case,  Fig.  145,  is  the  junction  point,  connecting  the 
front  and  rear  axle  drive  shafts,  the  driving  sprocket,  by  means 
of  a  silent  chain,  delivering  power  to  the  sprocket,  to  which  the 
fore  and  aft  shafts  are  attached.  The  shaft,  on  which  the  driving 
sprocket  is  mounted,  carries  a  brake  drum,  which  forms  the  service 
brake,  acting  on  all  four  wheels.  Emergency  brakes  are  on  the 
rear  wheels.  The  vehicle  is  steered  by  the  front  wheels  only,  in 
the  usual  manner. 

Live-axle  Drives. — Another  type  of  four-wheel  drive  construc- 
tion is  that  employing  a  live  front  and  rear  axle ;  that  is,  an  axle 
which  both  propels  the  car  and  carries  the  weight  of  the  vehicle 
and  load.  The  F.W.D.  and  Nevada  trucks  are  of  this  type. 

In  the  F.W.D.  chassis,  the  transmission  is  centrally  located 
with  a  very  broad,  silent  chain,  which  transmits  the  power  to  a 
shaft  parallel  to  and  far  enough  to  one  side  of  the  transmission 
to  permit  proper  clearance  between  the  engine  and  propeller 


FRONT-  AND  FOUE-WHEEL  DRIVES 


169 


shaft.  Each  of  the  two  propeller  shafts  carries  a  brake  drum,  so 
that  the  braking  force  is  applied  to  all  four  wheels.  Steering  is 
by  the  front  wheels  only,  so  that  the  rear  axle  is  of  conventional 
full-floating  design  with  bevel-gear  drive,  excepting  that  the  dif- 
ferential housing  is  located  to  the  left  of  the  axle  center. 


FIG.  146.     F.W.D.  Front  Axle. 

The  steering-knuckle  pivot  of  the  front  axle  (Fig.  146)  is  in 
the  form  of  a  spherical  joint,  which  has  two  trunnions,  one  on  the 
upper  side  and  one  on  the  lower  side,  so  that  only  a  pivoting 
action,  instead  of  a  universal  action  is  obtained.  A  divided  hous- 
ing surrounds  these  joints,  to  which  is  bolted  the  spindle,  upon 
which  the  wheel  revolves.  This  pivot  and  wheel  spindle  are  hol- 


FIG.  147.     Nevada  Front  Wheel  Drive. 


170    MOTOK  TRUCK  DESIGN  AND  CONSTRUCTION 

low  and  contain  the  drive  shaft  and  universal  joint.  The  center 
of  this  universal  is  in  line  with  the  center  of  the  wheel  pivot  and 
the  shaft  from  one  end  extends  into  the  differential,  while  the 
other  end  has  a  square,  which  fits  into  the  flange  that  drives  the 
wheel. 

In  the  Nevada,  the  steering  is  also  by  front  wheels  only.  The 
general  application  of  the  power  to  the  front  wheels  differs  some- 
what from  the  above,  although  this  design  also  employs  full- 
floating  axles.  In  this  vehicle,  the  differential  in  the  axles  is 
located  to  the  left  of  the  center  and  the  front  axle  has  a  somewhat 
different  power-transmitting  device  in  the  steering  knuckle. 

The  steering  knuckles  (Fig.  147)  are  similar  to  the  usual  type, 
consisting  of  a  yoke  at  the  end  of  the  axle  tube,  through  which 
passes  a  king  bolt,  on  which  revolves  a  solid  wheel  spindle.  On 
the  knuckle,  which  surrounds  the  king  bolt,  is  revolvably  dis- 


FIG.  148.     Couple  Gear  Electric  Drive. 

posed  a  double  bevel  pinion.  The  lower  teeth  of  this  bevel  pinion 
are  engaged  by  a  bevel  at  the  end  of  the  axle  shaft,  which  is  dis- 
posed within  the  axle  tube.  The  upper  teeth  mesh  with  a  larger 
bevel  gear,  this  being  fastened  to  a  stub  shaft  extending  through 
the  wheel  to  the  outer  edge  of  the  hub.  The  end  is  squared  and 
engages  the  driving  flange,  which  drives  the  wheel. 

In  the  chain-driven  vehicles,  the  thrust  and  torque  are  taken 
by  the  conventional  radius  rods,  while  the  remainder  are  divided 
between  spring  and  radius  rod  construction.  This  is  also  true  of 
differentials,  as  some  use  three  and  others  two,  in  compensating 
for  the  division  of  power  between  the  wheels. 


FEONT-  AND  FOUE-WHEEL  DEIVES  171 

Electric  Drive. — The  fourth  type,  or  electric,  is  particularly 
adaptable  to  one,  two  or  four-wheel  drives,  and  affords  a  very 
simple  construction  mechanically.  The  Couple  Gear  Freight 
Wheel  Company  makes  a  type  of  road  wheel,  which  is  constructed 
from  two  steel  discs,  between  which  is  mounted  an  electric  motor. 
This  wheel  (Fig.  148)  can  be  attached  to  an  axle,  regardless  of 
whether  or  not  it  is  pivoted.  This  company  builds  two  types  of 
trucks,  one  straight  electric  and  the  other  gasoline  electric.  In 
the  former,  batteries  are  used  to  supply  the  current  to  the  motors 
in  the  wheels,  while  in  the  latter  type,  a  gasoline  engine  drives  an 
electric  generator,  which  furnishes  the  current  consumed  by  the 
motors,  in  driving  the  wheels.  The  motor  is  carried  by  the  steer- 
ing knuckle,  the  armature  having  a  pinion  at  each  end,  one  pinion 
pulling  up  on  one  side  and  the  other  pulling  down  on  the  oppo- 
site side  and  both  mesh  with  large  ring  gears  attached  to  the  two 
discs  of  the  wheel,  ^his  affords  a  single  reduction  of  twenty- 
five  to  one.  A  device,  which  is  termed  an  "  evener,"  permits  of 
compensating  movements  and  divides  the  force  equally  between 
the  two  pinions,  regardless  of  any  unequal  wear  or  adjustments. 

Both  front-wheel  drives  and  four-wheel  drives,  are  capable  of 
further  developments,  and,  if  demands  for  these  types  of  vehicles 
continue,  we  may  expect  to  see  considerable  improvement  in 
details. 


CHAPTEE   XII 

MOTOR  TEUCK  BRAKES 

FROM  what  has  been  said  of  the  brakes  in  discussing  the  final 
drive  and  the  various  methods  of  applying  the  power  to  the  road 
wheels,  it  can  readily  be  understood  that  there  would  be  little  uni- 
formity as  regards  brake  construction  and  location,  except  that 
all  states  have  laws  which  specify  that  vehicles  must  be  equipped 
with  two-brake  systems — one  system  for  ordinary  service  and  one 
for  emergency.  In  horse-drawn  vehicles,  the  brakes  are  applied 
directly  to  the  steel  tires;  however,  since  rubber  is  quite  ex- 
pensive, this  method  of  brake  application  is  not  commercially 
possible;  but  it  is  effectively  accomplished  by  securing  to  the 
wheels  a  metal  drum,  on  which  the  friction  members  act. 

Until  recently  more  attention  has  been  given  to  acceleration 
of  the  commercial  car  than  to  the  retarding  forces  at  the  driver's 
disposal.  This  subject  at  present  is  receiving  considerable  study, 
which  is  evident  by  the  variety  of  types  and  the  numerous  loca- 
tions. The  brakes  are  invariably  applied  to  the  rear  wheels,  as 
they  present  considerable  advantage,  supporting  the  greatest  por- 
tion of  the  vehicle  and  load. 

On  vehicles  employing  the  double  side-chain  drive,  it  has  been 
considered  good  practice  to  place  one  set  of  brakes  on  the  jack- 
shaft  and  one  set  in  the  rear  wheels.  There  are  various  positions 
for  this  brake,  either  inside  or  outside  of  the  frame.  This  type  of 
brake  can  be  made  light  and  powerful,  but  possesses  other  disad- 
vantages which  have  led  some  makers  to  place  both  brakes  in  the 
rear  wheels.  On  shaft-driven  vehicles,  one  brake  can  be  mounted 
either  at  the  front  or  rear  end  of  the  propeller  shaft  and  one  set 
in  the  wheels,  or  both  sets  may  be  placed  in  the  wheel  drums. 

Locations. — Rear- wheel  brakes  for  either  type  of  final  drive 
may  be  divided  into  three  general  arrangements,  viz.,  two  in- 
ternal brakes  on  the  same  drum,  one  internal  and  one  external 
brake  on  the  same  drum  and  one  external  and  one  internal  or  two 
internal  brakes  operating  on  concentric  drums. 

Types. — There  are  two  general  types  of  brakes — the  band  and 
shoe  types,  and  either  may  be  made  external  contracting  or  in- 

172 


MOTOR  TRUCK  BRAKES 


173 


ternal  expanding.  The  band  type  consists  of  a  continuous  steel 
band  having  a  fabric  frictional  facing,  while  the  shoe  type  may 
either  be  of  cast  iron  with  a  high  percentage  of  manganese,  of 
phosphor  bronze  with  cork  inserts,  or  provided  with  a  fabric 
facing. 

When  frictional  facings  are  not  used,  the  shoes  are  provided 
with  diagonal  grooves  to  prevent  chattering  and  squeaking. 
Each  type  presents  a  variety  of  constructions,  as  regards  anchor- 
age, adjustments,  and  operating  mechanism.  In  addition  to  the 
brakes  acting  on  the  rear  wheels,  the  Saurer  motor  brake  can  also 
be  mentioned. 

The  writer,  in  discussing  this  subject,  will  endeavor  to  cover 
the  principal  types  in  use  and  in  conclusion  outline  their  advan- 
tages and  disadvantages. 

Considering  first  the  chain-driven  vehicles,  we  find  two  loca- 
tions for  the  service  brake,  either  outside  or  inside  of  the  frame. 


FIG.  149.     Knox  Jack  Shaft  Brake. 

Jackshaft  Brakes. — Fig.  149  serves  to  illustrate  the  jackshaft 
brake  used  on  the  Knox  tractor.  This  is  of  the  shoe  type  mounted 
outside  of  the  frame  and  is  anchored  to  the  frame  side  rail  by 
heavy  brackets.  Like  all  jackshaft  brakes,  this  is  of  the  high- 
speed type  and  equipped  with  two  cast  iron  brake  shoes,  which 
are  easily  removed  for  renewal  and  mounted  on  large  supports, 
while  ample  adjustment  is  provided  through  the  rod  connecting 
the  two  shoe  supports  with  the  operating  lever.  The  brake  drum 
is  made  from  cast  steel  and  is  fourteen  inches  in  diameter  with 
four-inch  face.  It  is  attached  to  a  hub  which  also  carries  the 


174    MOTOK  TRUCK  DESIGN  AND  CONSTRUCTION 

driving  sprocket.  Features  worthy  of  attention  in  connection 
with  this  construction  are  the  particular  attention  paid  to  the 
strength  of  the  brake  anchorage  and  the  unusual  provision  for 
cooling  presented  by  the  twenty  ribs  on  the  brake  drum. 

Hydraulic  Rear-wheels  Brakes. — The  rear-wheel  brakes  are 
perhaps  the  largest  ever  attempted  and  are  20  ins.  in  diameter 
with  a  6^-in.  face.  They  consist  of  steel  shoes  lined  with  friction 
fabric  and  hydraulicallly  operated.  This  hydraulic  mechanism 
is  of  ingenious  design,  so  that  there  is  practically  no  difference  in 
their  operation  from  the  ordinary  hand  brakes.  A  pump  lever 
takes  the  place  of  the  ordinary  hand  lever  and  a  button  for  the 
release  of  the  brake.  To  apply  the  brakes,  the  operator  makes 
two  or  three  full  strokes  with  the  handle  forward  and  backward 
and  the  application  of  the  brake  will  then  be  felt  in  the  form  of  a 
resistance  pulling  the  lever  backwards,  the  same  as  with  the  hand 
lever.  After  the  resistance  is  felt  a  good  hard  pull  on  the  handle 
will  lock  the  rear  wheels.  The  release  is  accomplished  by  push- 


FIG.  150.     Kelley  Internal  Expanding-  Rear  Wheel  Brake. 

ing  the  button  on  the  top  of  the  handle  and  pushing  the  handle 
forward  beyond  the  stop  normally  interposed.  Passing  beyond 
this  stop  exposes  a  release  part  in  the  pump,  which  allows  the 
liquid  to  flow  back  through  the  pump  into  the  reservoir. 

Most  any  of  the  following  brake  constructions  can  be  applied 
to  the  jackshaft,  while  they  may  be  placed  either  outside  of  the 
sprocket,  between  sprocket  and  frame  and  as  mentioned  pre- 
viously inside  of  the  frame. 


MOTOE  TKUCK  BRAKES 


175 


Rear-wheel  Brakes  on  Chain-drive  Models. — When  both  brakes 
are  located  in  the  rear  wheels,  they  are  generally  of  the  internal 
expanding  type.  The  reason  for  this  is,  should  an  external  brake 
become  disarranged,  the  chain  and  other  parts  may  be  injured, 
due  to  the  brake  mechanism  being  caught  in  the  chain  or  sprocket. 

The  Kelly  and  Natco  trucks  are  examples  of  this  type.  The 
Kelly  brake  construction,  shown  in  Fig.  150,  presents  an  excellent 
arrangement  and  possesses  several  features.  These  brakes  are  of 
the  shoe  type,  located  side  by  side,  lined  with  a  friction  fabric, 


BfiAHf 


FIG.  151.     Natco  Double  Eear  Wheel  Brake. 

and  operated  by  a  combination  toggle  and  eccentric.  Each  set  of 
shoes  are  hinged  on  liberal  eyed  pins  and  anchored  to  the  brake 
spider,  which  is  attached  to  the  radius  rod.  A  toggle  action, 
operated  by  an  eccentric  or  cam,  expands  the  front  end  of  the 
shoes,  while  the  tubular  shafts,  operating  the  eccentrics,  extend 
through  the  brake  spider  flange  extensions  and  are  keyed  at  the 
outer  ends  of  the  worm-wheel  operating  levers.  This  feature 
places  the  brake  adjustment  outside  of  the  wheel  so  that  adjust- 
ment can  be  obtained  without  removing  the  wheels.  Another 
feature  is  the  provision  of  large  grease  cups  arid  liberal  grooves 
for  lubricating  the  various  shaft  bearings. 

The  Nacto  Brakes  (Fig.  151)  are  also  of  the  lined-shoe  type; 
however,  they  differ  from  the  above  in  that  they  are  cam  actuated 
and  have  their  adjustment  incorporated  in  the  brake  linkage. 
Each  pair  of  shoes  is  hinged  to  the  spider  at  one  end,  while  the 
other  end  carries  hardened  steel  plates,  against  which  the  cam 


176    MOTOK  TRUCK  DESIGN  AND  CONSTRUCTION 

bears  in  expanding  the  shoes.  The  shoes  are  not  rigidly  attached 
to  the  hinge  pins,  but  are  free  to  move  and,  in  applying  the 
brake,  the  forward  end  engages  the  drum  first,  so  that  this  free 
end  permits  the  shoe  to  engage  more  evenly  at  all  points  of  its 
circumference. 

Brakes  on  Shaft-drive  Models. — The  two  brake  locations  in 
the  shaft-drive  vehicle  are  on  the  propeller  shaft  and  rear  wheels, 
or  both  in  the  rear  wheels.  This  applies  to  either  bevel,  double 
reduction,  internal  gear,  or  worm  drive,  the  bevel  and  double  re- 
duction axles  universally  using  the  double  rear- wheel  brake. 


FIG.  152.     Fierce-Arrow  Propeller   Shaft  Brake. 

Propeller-shaft  Brake. — The  Fierce-Arrow  worm-drive  trucks 
offer  an  excellent  example  of  the  propeller  shaft  brake.  This 
brake  (Fig.  152)  is  located  immediately  back  of  the  transmission 
and  anchored  to  a  frame  cross  member.  In  this  type,  two  cast- 
iron  shoes  are  brought  to  bear  against  the  cast  steel  brake  drum. 
These  shoes  are  hinged  to  arms  on  each  side  of  the  drums,  these 
arms  in  turn  are  hinged  to  a  bracket,  which  is  attached  to  the 
bottom  of  the  cross  member,  the  top  ends  pivoting  on  the  op- 
erating shaft.  Springs  are  placed  on  the  operating  shaft,  between 
these  two  arms,  to  keep  the  brake  released.  Mounted  on  the 
operating  shaft,  is  a  ratchet,  which  is  prevented  from  turning  by 
a  tongue  fitting  into  a  groove  in  one  arm.  The  brake  lever  has 
an  integral  ratchet,  which  meshes  with  the  ratchet  mounted  on 
the  operating  shaft,  forming  a  means  of  applying  the  brake.  A 
nut  is  placed  at  the  other  end  of  the  operating  shaft,  forming  the 
brake  adjustment.  The  drum  has  an  integral  ratchet,  and  a  pawl 
lever  is  attached  to  the  lower  link,  being  held  erect,  out  of  en- 


MOTOK  TKUCK  BRAKES 


177 


gagement  by  a  spring.  This  forms  a  ratchet  type  of  sprag  for 
locking  the  wheels  on  steep  hills  and  removes  the  strain  from  the 
brakes. 

The  Packard  worm  drive  and  G.V.  internal  gear-drive  trucks 
also  employ  the  transmission  brake,  while  the  Mais,  Fremont- 
Mais  and  3|-ton  Republic  internal  gear-driven  trucks  have  the 
service  brake  mounted  on  the  pinion  shaft  and  anchored  to  the 
axle  housing. 


FIG.  153.     The   Sheldon  Internal  Expanding-  Brake. 

Band  Brake.— The  Sheldon  brake  (Fig.  153)  illustrates  a 
simple  band  brake,  sometimes  called  a  single  expanding  shoe, 
operated  by  a  toggle  linkage.  This  type  of  brake  is  used  on  this 
company's  worm-drive  axles,  being  located  side  by  side  in  the 
rear-wheel  drums.  The  bands  are  supported  by  three  brackets 
bolted  to  the  brake  spider,  which  carries  the  operating  levers  and 
shafts.  The  bands  are  expanded  through  small  links  attached  to 
brackets  riveted  to  them  and  a  long  link  attached  to  the  lever  on 
the  operating  shaft.  A  large  stud,  located  in  the  spider,  prevents 
them  from  rotating.  A  coil  spring  releases  the  bands  and  holds 
the  brackets  in  contact  with  the  stud.  Adjustment  is  made 
through  the  brake  linkage  and  one  of  the  toggle  links. 
13 


178    MOTOE  TEUCK  DESIGN  AND  CONSTEUCTION 

Internal  and  External  Brakes. — The  Clark  Equipment  Com- 
pany offer  an  excellent  example  of  internal  and  external  rear- 
wheel  brake  (Fig.  154)  in  the  construction  employed  on  its  inter- 
nal gear-driven  axles.  The  external  brake  is  anchored  to  one  end 
of  the  brake  spider  while  the  other  end  is  provided  with  a  simple 
adjustment  for  taking  up  the  wear  of  the  lining.  The  internal 
brake  band  is  also  lined  with  a  friction  fabric  and  expanded  by 
a  cam.  This  cam  operates  on  hardened  steel  plates,  set  into  the 


ADJUSTMENT 


ADJUSTMENT 


FIG.  154.     Clark  Internal  and  External  Brakes. 

brake  band  brackets  and  so  arranged  that  they  can  easily  be  re- 
newed. The  forward  end  of  the  brake  is  supported  by  an  exten- 
sion of  the  brake  spider  and  has  liberal  provisions  for  adjustment. 
An  excellent  feature  in  connection  with  this  brake  is  the  pro- 
vision of  a  metal  disc  and  packing  separating  the  gear  compart- 
ment from  that  of  the  internal  brake.  This,  in  addition  to  mak- 
ing it  possible  to  lubricate  the  gears  with  graphite,  guards  against 
the  breakage  of  the  gears  in  case  any  part  of  the  brake  mechan- 
ism should  come  loose. 


MOTOK  TEUCK  BKAKES 


179 


Another  good  example  of  internal  and  external  brake  con- 
struction is  shown  in  Fig.  155  and  used  on  the  Autocar.  The  ex- 
ternal brakes  are  of  the  double  shoe  type,  fabric-lined  and  hinged 
to  a  stud  projecting  from  the  brake  spider,  and  small  clevises, 
attached  to  the  spider,  hold  the  shoes  longitudinally  on  the  drum. 
They  are  connected  at  the  front  end  by  a  rod,  which  forms  the 
adjustment  and  also  carries  the  springs  to  release  the  brake.  The 


FIG.  155.     Autocar  Internal  and  External  Brakes. 

internal  brakes  are  also  of  the  shoe  type,  fabric-lined  and  hinged 
to  the  brake  spider.  They  are  expanded  by  a  double-armed  lever 
which  is  connected  to  them  by  links.  This  lever  is  similar  to  a 
bell  crank,  with  pins  extending  laterally  from  the  ends  of  its 
arms,  to  which  the  links  are  attached. 

Concentric  Brakes.— The  G.M.C.  construction,  Fig.  156,  de- 
picts a  type  employing  concentric  drums.  The  internal  brake  is 
of  the  conventional  shoe  type,  fabric-lined,  expanded  by  a  cam 
and  operating  on  the  inner  drum.  The  external  brake  operates 
on  the  outer  drum,  being  of  the  band  type  and  contracted  by  a 


180    MOTOE  TKUCK  DESIGN  AND  CONSTEUCTION 

double-armed  lever.  This  double-armed  lever  is  formed  integral 
with  the  operating  shaft  and  is  slotted  to  receive  the  band  bracket 
and  the  clevis  rod,  which  carries  the  releasing  spring  and  also 
forms  the  adjustment. 


FIG.  156.     G.M.C.  Concentric  Brakes. 

The  Timken  Duplex  Brake. — The  Timken  Detroit  Axle  Com- 
pany has  recently  introduced  a  new  type  of  brake  (Fig.  157)  on 
its  worm-drive  axles,  which  is  termed  a  "  duplex  brake."  These 
brakes  consist  of  four  fabric-lined  shoes,  located  in  such  a  manner 
that  the  pair  of  brakes  takes  up  but  little  more  room  than  a  single 
brake  of  ordinary  shoe  type.  These  four  shoes  are  equally  spaced 
on  the  inner  circumference  of  the  brake  drum  and  each  pair 
located  diametrically  opposite  are  expanded  by  cams  and  sup- 
ported by  the  brake  spider  and  large  pins.  One  pair  of  shoes 
has  single  arms,  which  extend  to  the  cam  and  its  support  and 
these  pass  between  two  arms  of  the  other  pair  of  shoes.  These 
shoes  are  made  somewhat  larger  in  width,  to  obtain  the  proper 
brake  area  and  are  held  longitudinally,  by  means  of  hardened 
steel  washers  on  the  operating  shaft  and  by  the  brake  spider. 

Any  one  of  the  brakes  described  above,  with  the  exception  of 
the  Pierce  and  Knox,  may  be  applied  to  a  chain-  or  shaft-driven 
vehicle  in  any  position  mentioned. 


MOTOR  TRUCK  BRAKES 


181 


Saurer  Motor  Brake. — Another  type  worth  mentioning  is  the 
Saurer  brake,  being  an  air  brake  worked  by  the  the  throttle  lever. 
For  a  quarter  of  a  circle  this  lever  controls  the  throttle,  but 
beyond  this  position,  through  a  device  incorporated  in  the  car- 
buretor, it  causes  the  motor  to  operate  on  the  two-cycle  principle, 
compressing  air  in  the  cylinders  to  an  extent  which  enables  the 
car  to  be  controlled  on  a  20  per  cent,  grade  without  the  need  of  a 
brake. 


FIG.  157.     Timken  Duplex  Brake. 

In  applying  any  type  of  brake,  it  must  be  held  from  rotating 
and  this  strain  is  generally  taken  by  the  brake  spider  which  rides 
free  on  the  axle  or  jackshaft  and  transmits  this  strain  to  the 
radius  rod  or  frame  on  the  chain-driven  vehicles  and  to  the  axle 
housing  on  shaft-driven  vehicles. 

Mounting  the  service  brake  on  the  jackshaft  or  propeller  shaft 
places  these  brakes  where  they  are  well  protected  and,  as  they 
are  of  the  high-speed  type,  the  reduction  through  the  chains  or 
gearing  makes  them  more  powerful.  This  presents  a  disadvan- 
tage, in  throwing  the  entire  braking  strain  on  the  chains  or  drive 
shaft  and  differential  and  thus  shortening  their  lives.  Should 
the  chains  or  drive  shaft  break  on  a  bad  hill,  and  the  emergency 


182    MOTOK  TRUCK  DESIGN  AND  CONSTRUCTION 

brakes  be  out  of  commission,  serious  damage  would  result.  Al- 
though this  may  rarely  occur,  some  makers  have  protected  their 
vehicles  against  such  accidents,  by  placing  both  sets  of  brakes 
in  the  rear  wheels,  thus  placing  the  retarding  force  as  near  as 
possible  to  the  point  where  the  momentum  of  the  vehicle  is 
checked.  In  a  sense,  this  argument  is  true,  especially  on  the 
heavier  vehicles,  for  the  fewer  elements  there  are  between  the  tire 
and  brake,  the  fewer  are  subjected  to  stress  and  the  fewer  are  the 
chances  of  failure. 

Brake  adjustments  are  also  receiving  considerable  study  and, 
while  in  some  cases  they  are  almost  hidden,  in  others  they  are 
very  accessible.  This  adjustment  may  either  be  incorporated  in 
the  brake  linkage  or  in  the  brake.  The  tendency  seems  to  be 
toward  locating  it  in  the  brake  in  such  a  manner  that  it  is  ac- 
cessible without  removing  the  wheel. 

Brake  equalizers  are  quite  common  on  commercial  cars,  the 
well-known  whippletree  type  being  quite  popular. 

When  a  single  brake  is  applied  on  the  propeller  shaft,  the 
differential  takes  care  of  the  distribution  of  force  to  the  two 
wheels  equally,  but  this  kind  of  compensation  has  a  disadvantage, 
in  that,  if  the  adhesion  of  the  two  wheels  is  greatly  different,  that 
with  the  slightest  grip  on  the  road  may  actually  cause  it  to  rotate 
backwards.  Still,  it  is  only  on  very  rare  occasions  that  this  re- 
verse motion  occurs  and  it  is  not,  therefore,  a  cause  of  much 
added  tire  wear. 

If  the  braking  forces  are  not  equalized,  the  task  of  adjusting 
the  brakes  is  much  more  difficult  than  it  need  be.  On  one  vehicle, 
the  whippletree  equalizer  is  replaced  by  a  diminutive  differential 
gear,  providing  a  smoother  action  and  a  much  larger  range  of 
equalization. 


CHAPTEE  XIII 

THE  FEONT  AXLE 

THE  front  axle  with  its  steering  gear,  knuckle  and  arms  is 
largely  depended  upon  for  the  safe  control  of  the  vehicle,  while 
it  must  also  carry  the  forward  portion  of  the  vehicle  and  load. 
It  must  be  so  arranged  as  to  permit  steering  the  car  and  in  order 
to  accomplish  this,  the  front  wheel  spindles  are  pivoted  in  the 
axle  end  and  are  held  in  proper  relation  to  each  other  by  a  tie 
rod,  which  connects  levers  extending  from  each  pivot.  Another 
lever  extends  from  either  right  or  left-hand  pivot  (depending 
upon  left  or  right-side  drive)  which  is  connected  by  a  drag  link 
with  the  steering  gear. 

This  pivot  is  termed  the  steering  knuckle  and  has  the  wheel 
spindle  formed  integral,  while  the  levers  may  either  be  formed 
integral,  or  attached  to  the  knuckle. 

Three  General  Types. — There  are  three  general  types  of  steer- 
ing knuckles,  known  as  the  Elliot,  Reversed  Elliot  and  Lemoine 
types.  In  American  practice  the  Elliot  type  is  most  extensively 
used  and  the  Lemoine  least.  In  the  Elliot  type  the  ends  of  the 
axle  proper  are  forked  and  the  steering  knuckle  is  T-shaped, 
while  in  the  reversed  Elliot  the  knuckle  is  forked  and  the  axle 
end  forms  a  T.  In  the  Lemoine  type  both  axle  end  and  knuckle 
form  L's.  In  practice  each  of  these  types  differ  somewhat,  de- 
pending upon  the  type  of  bearings  and  the  method  of  mounting 
the  knuckle  in  the  axle  end. 

For  some  time  it  was  the  general  impression  that  when  the 
plane  of  the  front  wheel  was  in  line  with  the  plane  of  the  knuckle 
pivot,  the  effect  of  road  inequalities  would  not  be  transmitted  to 
the  steering  gear.  This  contention  led  to  the  introduction  of  a 
type  of  knuckle  in  which  the  wheel  center  lies  very  close  to  the 
pivot  center. 

The  knuckle  in  this  type,  instead  of  having  a  T-shape,  in- 
cludes a  sort  of  a  yoke  extending  outside  of  the  wheel  hub  to 
points  close  to  the  spokes  and  the  forked  axle  ends  are  pivoted  to 
the  yokes  at  these  points.  However,  this  is  of  minor  importance, 
since  the  speed  of  commercial  cars  is  comparatively  low  and  with 
a  semi-reversible  gear  the  road  shocks  are  not  transmitted  to  the 

183 


184    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

steering  wheel.  One  prominent  maker  employed  this  type  of 
knuckle  for  a  number  of  years,  but  has  discarded  it  and  is  now 
using  the  Elliot  type. 

The  levers  to  which  are  attached  the  tie  rod  used  for  connect- 
ing the  two  knuckles  and  the  one  for  connection  with  the  steering 
gear  are  known  as  knuckle  arms.  These  may  either  be  formed 
integral  with  the  knuckles,  or  attached  by  means  of  a  taper  and 
keyway,  retained  by  a  castellated  nut.  One  prominent  maker 
forms  the  spindle  and  levers  separately  so  that  they  may  be  dove- 
tailed together  and  retained  by  the  pivot  pin.  The  general  prac- 
tice is  to  attach  them  to  the  knuckles  since  this  simplifies  manu- 
facturing and  replacement. 

Owing  to  their  importance,  the  knuckles  and  arms  are  always 
forged  from  a  good  quality  of  steel  and  heat  treated.  The  tie  rod 
may  either  be  placed  in  front  or  in  the  rear  of  the  axle,  while  the 
steering  connection  may  either  be  arranged  for  cross  or  fore  and 
aft  steering.  The  arrangement  of  tie  rod  and  steering  connections 
depend  upon  the  general  construction  of  the  vehicle  and  the  loca- 
tion of  the  steering  gear. 

The  Axle  Proper. — The  axle  proper  may  either  be  forged  from 
medium  ca,rbon  steel  of  solid  rectangular  section  or  of  I-beam 
section,  approaching  a  full  rectangular  section.  Cast  steel  axles 
are  also  used,  while  one  maker  of  a  popular  priced  vehicle  uses 
cast  steel  ends  with  a  round  section  center.  These  axles  may  also 
be  built  up  with  tubular  centers,  flat  plates  riveted  together,  or 
from  pressed  steel  of  channel  section. 

Attachment  to  Frame. — In  conventional  designs  the  only  con- 
nection between  the  axle  and  the  frame  is  through  the  front 
springs,  which  with  few  exceptions  are  of  the  semi-elliptic  type. 
One  maker  uses  a  full  elliptic  front  spring  and  provides  a  dis- 
tance rod  to  hold  the  axle  in  alignment  with  the  frame. 

Fig.  158  illustrates  a  front  axle  with  cast  steel  center  for  light 
delivery  cars  of  750  to  1,000  Ibs.  capacity.  The  center  is  dropped 
considerably,  that  is,  the  topmost  surface  of  the  axle  bed  is  located 
considerably  below  the  center  of  the  wheel  spindle,  since  it  is  in- 
tended for  use  with  full  elliptic  front  springs  and  pneumatic 
tires.  The  knuckle  is  of  the  Elliot  type  and  drop -forged  with 
integral  spindle  and  has  a  boss  at  its  lower  end  which  is  provided 
with  taper  and  keyway  for  attaching  the  knuckle  arm.  The  tie 
rod  is  placed  to  the  rear  of  the  axle  center  and  is  attached  to  the 
knuckle  arms  by  a  clevis  and  bolt.  The  knuckles  are  arranged  for 


THE  FEONT  AXLE 


185 


cross  steering  and  one  clevis  bolt  has  an  extension  which  carries  a 
cross  to  which  the  drag  link  is  attached.  This  cross  serves  as  a 
universal  coupling  to  compensate  for  the  angular  positions  of  the 


CUP  f CON£ 
BALL  BEARING 


FIG.  158.     Light  Truck  Axle  with  Cast  Center. 

knuckle  arms  and  the  variation  in  the  vertical  movement  between 
axle  and  frame.    This  is  necessary  as  the  steering  gear  is  always 


FIG.  159.     Vulcan  5-Ton  Front  Axle. 

attached  to  the  frame  and  the  action  of  the  springs  tend  to  vary 
the  distance  between  the  frame  and  the  axle.  The  hubs  are  mal- 
leable castings  with  flanges,  which  hold  the  spokes  of  the  wheel. 


186    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


Cup  and  cone  ball  bearings  are  used  for  mounting  the  hubs  on 
the  spindle.  Bearing  adjustment  is  by  means  of  a  nut  on  the 
spindle  and  spacing  washers. 

The  Vulcan  Front  Axle. — The  Vulcan  five-ton  axle  (shown  in 
Fig.  159)  offers  an  example  of  heavy  vehicle  construction  ar- 
ranged for  fore  and  aft  steering,  with  the  tie  rod  located  to  the 
rear  of  the  axle. 

The  axle  center  is  a  drop  forging  with  integral  spring  seats. 
These  spring  seats  are  placed  as  close  as  possible  to  the  wheel 
center  in  order  to  obtain  the  maximum  capacity.  The  stress,  due 
to  both  the  combined  weight  of  the  vehicle  and  its  load  and  that 
due  to  the  wheel  striking  an  obstruction,  increases  from  nothing 
at  the  center  of  the  wheel  to  a  maximum  at  the  center  of  the 
spring  seat.  For  this  reason  a  minimum  distance  is  desired.  It 
is  customary  to  increase  the  section  of  the  axle  center  between  the 
knuckles  and  spring  seat  centers,  both  in  a  vertical  and  horizontal 
plane  to  withstand  this  stress.  The  knuckles  on  this  axle  are  also 
of  the  Elliot  type,  but  instead  of  forging  the  spindle  integral  with 
the  knuckle  pivot  and  keying  the  arms  to  the  former,  these  parts 

are  forged  separately  and 
keyed  together  by  integral 
keys.  The  pivot  pin  has 
a  shoulder  at  one  end  and  a 
nut  at  the  other  end  to 
hold  them  together  and  the 
entire  unit  is  supported 
by  bushings  and  thrust 
washers  in  the  fork  of  the 
axle  center.  The  hub  con- 
struction is  of  conventional 
design,  employing  annular 
ball  bearings  for  wheel 
mounting. 

The     Peerless     Axle.— 

Fig.  160  depicts  the  Peer- 
less   front    axle,    which    is 
built     along     conventional 
lines  with  drop  forged  cen- 
ter, integral  spring  seats  and  Elliot  type  knuckles.    In  detail,  this 
construction  differs  from  those  mentioned  above  in  that  the  bush- 
ings for  supporting  the  pivot  pin  are  located  in  the  knuckle  in- 


FIG.  160.     Peerless  Front  Axle. 


THE  FKONT  AXLE 


187 


stead  of  in  the  axle  fork.  Thrust  washers  are  replaced  by  a  ball- 
thrust  bearing,  located  in  the  upper  part  of  the  fork.  The  steer- 
ing arm  is  forged  integral  with  the  knuckle  arm  and  attached  to 
the  knuckle  by  a  taper  and  key.  The  steering  arm  being  so  ar- 
ranged as  to  clear  the  lower  surface  of  the  center.  The  front 
wheels  are  mounted  upon 
Timken  roller  bearings  and 
dished,  that  is,  the  wheel 
spokes  are  set  at  angles 
with  a  plane  perpendicular 
to  the  axis  of  the  wheel. 

The  Timken  Front  Axle 
(Fig.  161)  is  used  on  a  num- 
ber of  commercial  cars.  It 
has  a  drop  forged  center  of 
I-beam  section,  and  Elliot 
knuckles.  The  axles  are 
arranged  for  either  type  of 
steering  to  meet  the  re- 
quirements of  vehicle  mak- 
ers. However,  in  this  case 
the  cross  steering  arrange- 
ment with  the  tie  rod  and 
drag  link  located  in  front 
of  the  axle  is  shown.  The 

knuckle  and  pivot  pin  are  locked  together  with  a  bolt,  so  that  this 
part  is  properly  supported  by  the  Timken  bearing  in  the  axle 
fork.  Timken  bearings  are  also  used  for  wheel  mounting. 

The  axles  mentioned  above  are  all  arranged  for  right-side 
steering,  while  the  Natco  axle  (Fig.  162)  arranged  for  left-side 
fore  and  aft  steering  with  the  tie  rod  located  at  the  rear  of  the 
axle.  It  is  of  conventional  design  with  Elliot  knuckles  and  pivot 
pin  bushings  located  in  the  knuckles.  This  illustration  shows 
how  the  center  is  dropped  to  provide  the  proper  clearance  between 
it  and  the  radiator  or  other  units  which  may  be  near  it.  It  also 
shows  the  method  of  providing  clearance  for  the  tie  rod  and  it 
will  be  noted  that  this  is  not  bent  to  the  shape  of  the  axle,  as  pro- 
vision must  be  made  to  compensate  for  the  movement  of  the 
knuckle  arms.  This  axle  is  an  example  of  light  truck  construc- 


FIG.  161. 


Plan  and  Side  View  of  Tim- 
ken  Front  Axle. 


188    MOTOR  TEUCK  DESIGN  AND  CONSTRUCTION 

tion,  and  also  presents  one  method  of  driving  the  speedometer  by 
gearing  from  the  wheel. 


STEEPING 
MOTION 
OF» 


FIG.  162.     Natco  Axle  Top  and  Side  Views. 

Pierce  Axle. — The  Pierce  worm-driven  trucks  are  equipped 
with  front  axles  having  reversed  Elliot  type  knuckles  and  fore 
and  aft  right-hand  steering.  The  axle  center  is  an  I-beam  section 


5TEER/NG  ARM 


FIG.  163.     Type  of  Front  Axle  used  on  Pierce- Arrow  Worm-Driven  Trucks. 

forging  and  is  perfectly  straight,  with  integral  spring  seats.  The 
pivot  pin  bushings  are  located  in  the  knuckles  and  so  arranged 
that  the  thrust  is  taken  by  the  shoulders  of  these  bushings  and  a 


THE  FRONT  AXLE 


189 


J 


FIG.  164.     Packard  Front  Axle. 


thrust  washer.    The  pivot  pin  has  a  taper  which  fits  into  the  axle 
center  so  that  it  can  be  drawn  up  tight  by  a  castellated  nut.    The 
wheels     are     mounted     on 
Timken  roller  bearings  as 
shown  in  Fig.  163. 

Packard  Axles.— The 
new  Packard  worm-driven 
trucks  are  equipped  with 
front  axles  (Fig.  164),  em- 
ploying the  reversed  El- 
liot type  of  knuckle;  how- 
ever, they  are  arranged  for 
left  side  fore  and  aft  steer- 
ing. The  axle  proper,  how- 
ever, is  dropped  at  the  center.  This  construction  is  similar  to  the 
one  depicted  above,  with  the  exception  of  the  steering  arms,  which 
are  attached  to  the  lower  part  of  the  knuckle.  This  permits 
proper  clearance  for  the  tie  rod  and  places  it  in  such  position  that 
it  is  not  necessary  to  bend  it.  A  feature  worthy  of  attention  on 
both  of  these  axles  is  the  provision  of  ball  and  socket  connections 
for  the  tie  rod  and  drag  link  in  place  of  the  more  customary  clevis 

and  bolt.  These  ball  and 
socket  joints  have  springs 
so  that  the  wear  in  the 
steering  connections  is  auto- 
matically taken  up. 

The  International  Har- 
vester Corporation  trucks 
for  some  years  had  used  the 
Sarven  type  of  wheel  in 
connection  with  an  Elliot 
type  of  steering  knuckle,  in 
which  the  pivot  center  lies 
very  close  to  the  center  of 
the  wheel.  This  is  shown 
in  Fig.  165  and  it  will  be 
noted  that  the  hub  construc- 
tion resembles  an  ordinary 
vehicle  wheel  hub.  This 
consists  of  wooden  hubs 

with  steel  hub  flanges,  the  former  have  steel  shells  which  carry  the 
wheel  bearings.     The  outer  wheel  bearing  is  of  the  roller  type 


FIG.  165.     Axle  used  on  some  of  the  In- 
ternational Harvester  Trucks. 


190    MOTOE  TKUCK  DESIGN  AND  CONSTRUCTION 

made  by  the  I.H.C.,  while  the  inner  bearing  consists  of  a  steel  and 
bronze  shell,  the  latter  having  a  taper  bearing  in  the  shell  in- 
serted in  the  wood  hub.  The  bronze  shell  is  provided  with  oil 
holes  and  grooves,  so  that  the  entire  bearing  can  work  in  graphite 
and  grease.  The  knuckle,  instead  of  having  the  usual  hub  for  the 
pivot  pin  or  king  bolt,  as  it  is  sometimes  called,  has  a  yoke,  which 
fits  into  the  axle  yoke.  Short  pins  pass  through  the  axle  and 
knuckle  yokes  to  form  the  pivot. 

The  above  axles  all  have  drop  forged  centers,  which  may 
either  be  forged  in  one  piece  or  the  two  ends  may  be  forged  sep- 
arately and  welded  together  at  the  center. 

The  Reo  Axle.— The  Reo  two-ton  front  axle  (Fig.  166)  differs 
from  those  shown  above  in  that  the  center  is  built  up  from  a  bar 
of  round  section,  pinned  and  brazed  into  cast  steel  ends  which 
form  the  forks.  The  knuckles  are  of  the  Elliot  type  and  carry 
the  bushings  for  the  pivot  pin.  The  knuckle  arms  fit  over  the 


FIG.  166.     Reo  2-Ton  Front  Axle. 

ends  of  the  knuckle  and  are  held  in  unison  with  knuckle  by  two 
keys.  This  axle  is  arranged  for  left-side  steering  and  the  tie  is 
placed  directly  back  of  the  axle  bed.  It  is  not  necessary  to  bend 
it,  since  ample  clearance  is  obtained  by  placing  the  spring  seats 
above  the  wheel  center.  The  wheels  are  mounted  on  Timken 
roller  bearings  and  retained  by  a  castellated  nut  and  keyed 
washer. 

Vim  and  Commerce  Axles. — The  Vim  and  Commerce  trucks 
also  employ  built-up  axles  with  Elliot  knuckles,  but  the  center 
or  bed  is  made  of  tubular  section.  The  Avery  farm  trucks  em- 
ploy another  type  of  built-up  front  axles.  A  malleable  casting 
forms  the  steering  head  to  receive  the  Lemoine  type  of  knuckle, 
which  is  equipped  with  a  series  of  hardened  steel  washers  to  take 
the  thrust. 


THE  FKONT  AXLE 


191 


FIG.  167.     Lemoine  Type  of  Knuckle. 


On  either  side  of  the  steering  head  extensions  are  riveted  a 
couple  of  steel  plates  as  shown  in  Fig.  167.  These  are  straight  at 
the  spring  seats  and  bent  up  slightly  at  the  ends  to  attach  to  the 
steering  head  castings. 
Blocks  are  placed  between 
the  two  axle  plates  di- 
rectly under  each  spring 
to  form  the  seat.  The 
steering  connections  are 
arranged  for  cross  steer- 
ing and  are  located  in 
front  of  the  axle. 

The  three-wheel  "Wayne 
Light "  commercial  car 
having  a  capacity  of  800 
Ibs.  also  employs  a  built- 
up  front  axle  as  shown  in  Fig.  168.  Two  sections  of  rolled  chan- 
nel steel  are  riveted  together  and  with  drop  forged  yokes  and 
Elliot  type  knuckles  at  either  end. 

Pressed  steel  centers  may  also  be  used,  while  combinations  of 
the  above  types  may  also  be  worked  out. 

Bearings. — All  American  trucks  are  equipped  with  anti-fric- 
tion bearings  such  as  the  ball  and  roller  types,  which  are  capable 
of  carrying  both  a  radial  and  thrust  load.  The  mounting  of 

these  bearings  presents  no 
difficulty  and  they  are  usu- 
ally provided  with  adjust- 
ments to  compensate  for 
wear.  The  tie  rods  and 

FIG.  168.     Wayne   Light  Axle,   Bnilt-Up   drag     links.   a1*6     made     °f 
Type.  tubular  section  and  are  pro- 

vided with  adjustments  so 

that  the  alignment  of  the  wheels  may  be  properly  maintained. 
Lately  there  seems  to  be  a  tendency  to  use  the  ball  and  socket 
joint  for  these  in  preference  to  the  clevis.  The  former  will  to  a 
considerable  extent  take  up  the  wear  automatically  and  can  also 
be  more  efficiently  lubricated. 


CHAPTEE  XIV 

STEERING  GEARS  AND  FUNDAMENTAL  PRINCIPLES  OF  STEERING 

MECHANISMS 

Certain  Principles  That  Must  be  Understood  in  Designing 
Them. — Some  interesting  problems  pertaining  to  the  design,  con- 
struction and  operation  of  the  modern  commercial  car  are  found 
in  the  various  steering  mechanisms  employed.  Like  almost  every 
other  important  mechanical  features,  the  steering  devices  now  in 
general  use  have  resulted  from  a  careful  study  of  the  conditions 
to  be  fulfilled,  supplemented  by  extensive  experiments  with  dif- 
ferent types.  These  researches  have  resulted  in  a  general  steering 
system  which  is  applied  in  different  forms  to  all  standard  com- 
mercial vehicles.  This,  in  brief,  consists  of  a  hand-wheel,  con- 
nected through  some  form  of  linkage  and  gearing  leverage  to 
the  front  wheels  of  the  vehicle,  these  wheels  being  carried  on 
pivoted  ends  of  the  front  axle.  The  design  and  construction  of 
some  of  the  most  important  features  of  this  general  arrangement 
afford  interesting  subjects  for  discussion. 

Throw  of  Front  Wheels. — Commercial  vehicles  must  neces- 
sarily be  operated  within  a  limited  space  such  as  a  narrow  street, 
and  it  is  of  importance  that  the  extreme  throw,  from  side  to  side 
of  the  front  wheels  be  settled  upon,  as  the  amount  of  this  throw, 
together  with  the  wheelbase  and  tread  determines  the  turning 
radius.  In  practice  the  latter  two  items  are  established  by  the 
load  or  body  requirements,  and  with  these  fixed,  the  throw  of  the 
front  wheels  is  usually  limited  by  the  width  of  the  body,  frame 
or  springs  and  the  permissible  distance  between  the  pivot  cen- 
ters about  which  the  wheels  swing.  The  angles  which  the  con- 
necting linkage  make,  become  too  acute  or  obtuse  according  to 
their  location,  if  the  maximum  throw  of  the  wheels  is  made  more 
than  35  degrees.  If  this  throw  is  exceeded,  steerage  is  difficult 
and  unsafe. 

The  theoretical  center  about  which  the  vehicle  turns  is  some- 
what in  the  center  line  of  the  rear  axle  prolonged,  the  exact  loca- 
tion being  determined  by  the  intersection  of  this  line  by  a  line 
drawn  normal  to  the  inside  front  wheel.  Another  line  drawn 
from  this  intersection  to  the  center  of  the  outside  front  wheel 

192 


STEEEING  GEARS 


193 


should  be  normal  to  this  wheel  if  it  is  at  the  correct  angle  to  pre- 
vent excessive  side  slip,  which  is  very  destructive  to  the  vehicle 


tire.    The  four  wheels  will  describe  concentric  circles  about  this 
theoretical  center.    This  is  clearly  illustrated  in  Fig.  169  and  it 
will  be  noticed  that  the  minimum  turning  radius  is  the  radius  of 
14 


194    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

the  arc  described  by  the  outer  front  wheel  when  these  wheels  are 
in  the  position  of  maximum  throw.  The  differential  device  allows 
the  proper  relation  of  speed  between  the  rear  wheels. 

The  outer  front  wheel  pivot  is  turned  a  smaller  angle  than 
the  inner,  and  they  are  connected,  by  a  cross  rod,  rigidly  attached 
to  them.  There  must  be  some  compensating  device  interposed  to 
give  the  same  angular  relation  when  the  wheels  are  turned  in  the 
opposite  direction.  This  is  accomplished  by  making  use  of  the 
principle  of  varying  ratios  of  sines  of  the  angles  at  different 


FIG.  170.     Arrangement   of  Knuckle   Levers  and  Tie  Eod  for  Front   and 

Rear  Positions. 

points  in  the  arcs  through  which  the  knuckle  levers  turn.  This 
necessitates  locating  the  pivot  or  knuckle  levers  so  that  their  cen- 
ters diverge  if  they  project  ahead  of  the  axle,  and  converge  if 
they  project  back  of  it.  As  the  wheels  swing,  the  knuckle  lever 
mounted  on  the  spindle  of  the  inner  wheel  travels  away  from  the 
dead  center  arc,  thus  traveling  a  smaller  angular  distance.  This 
is  illustrated  by  heavy  lines,  Fig.  170,  which  are  shown  for  both 
front  and  rear  location  of  the  cross-rod. 

Knuckle  Lever  Angles. — There  are  various  methods  of  theo- 
retically determining  the  proper  angles  of  these  levers,  either 
mathematically  or  graphically;  however,  this  is  largely  a  matter 
of  compromise,  between  what  is  theoretically  correct  and  what  is 
attainable  practically.  Some  makers  follow  the  practice  of  lay- 
ing out  these  steering  connections  so  that  the  center  line  of  the 
knuckle  lever  extended  will  intersect  the  center  of  the  rear  axle. 
Others  endeavor  to  obtain  a  knuckle  lever  length  and  angle,  that 
while  fitting  into  the  general  layout  of  the  vehicle,  gives  the 


STEEEING  GEARS  195 

largest  possible  range  of  steering  angle  without  undue  error. 
This  is  generally  determined  more  by  experience  than  by  any 
figures.  Another  point  which  must  be  considered  in  the  general 
layout,  is  the  various  lengths  of  wheel  bases  and  this  suggests 
making  the  angle  of  the  knuckle  levers  as  small  as  possible,  con- 
sistent with  reasonable  clearance  between  the  ends  of  the  cross 
tube  and  the  spokes  of  the  wheels. 

Location  of  Knuckle  Levers. — Both  front  and  rear  positions 
of  these  two  levers  are  used  and  each  position  possesses  its  ad- 
vantages and  disadvantages.  Some  makers  prefer  the  forward 
location  for  the  reason  that  it  enables  large  steering  angles  to  be 
used  safely,  thus  diminishing  the  turning  radius  of  the  vehicle. 
With  the  rear  position  the  tie-rod,  connecting  these  two  levers,  is 
better  protected  from  injury,  providing  the  proper  clearance  can 
be  obtained  under  the  engine  base.  The  length  of  this  tie-rod  is 
so  adjusted  that  with  the  front  wheels  in  the  central  position  the 
distance  apart  of  the  wTheel  felloes  at  the  height  of  the  spindle  is 
from  3/16  in.  to  5/8  in.  less  in  front  of  the  axle  than  back  of  it. 
The  amount  of  toe-in  depends  upon  the  diameter  of  the  wheel, 
the  lower  figures  being  used  for  wheels  34  ins.  or  less.  This 
toeing-in  is  intended  to  allow  for  slight  play  in  the  joints  of  the 
tie-rod  and  the  flexure  of  its  members.  It  is  also  intended  to  cor- 
rect the  tendency  of  the  wheels  to  toe  outward  when  the  vehicle 
is  moving. 

Inclination  of  the  Wheel  Spindles. — The  spindle  upon  which 
the  wheel  revolves  is  generally  inclined  from  1^  to  2  degrees 
below  the  horizontal  center,  while  the  king  bolt  about  which  the 
wheel  pivots  is  brought  as  close  to  the  spokes  as  possible,  in  order 
to  bring  the  point  of  intersection  of  the  center  of  the  wheel  with 
the  ground  as  close  to  the  center  of  the  bolt  produced  as  possible. 
This  distance  forms  the  lever  arm  at  the  end  of  which  the  re- 
sistance to  motion  of  the  front  wheels  acts  when  the  wheels  swing 
around  for  steering. 

To  approximate  castor  steering,  some  manufacturers  also  in- 
cline the  axles  and  king  bolt  in  a  fore  and  aft  plane,  as  in  Fig. 
171,  the  inclination  being  about  four  degrees  on  the  average.  The 
reasons  for  these  features  are  that  they  make  steering  easier,  in 
that  the  construction  produces  a  trailer  effect  which  tends  to  ob- 
viate serious  consequences  in  the  event  of  breakage  or  disconnec- 
tion of  the  steering  linkage.  The  point  of  wheel  contact  with  the 
ground  is  behind  the  point  at  which  the  center  of  the  king  bolt 


196    MOTOK  TEUCK  DESIGN  AND  CONSTRUCTION 


FIG.  171.  Trailer  Effect  when  Cas- 
tor Steering  is  Approximated  by  In- 
cluding King  Bolt. 


produced  meets  the  ground,  hence  the  steering  wheels  trail  and 
are  automatically  kept  in  the  straight  ahead  position  by  the  road 

resistance.  This  trailer  ef- 
fect somewhat  reduces  wob- 
bling of  the  front  wheels  and 
also  reduces  the  shock  on  the 
steering  gear. 

Reversibility  of  Steering 
Gears. — To  prevent  road 
shocks  from  being  trans- 
mitted to  the  operator's 
arms,  it  is  considered  best  to 
have  the  steering  gear  back- 
locking,  or  irreversible  to 
some  extent  at  least.  With 
a  perfectly  reversible  system 
it  is  evident  road  shocks, 
which  are  transmitted  to  the 
operator's  hands,  depend 
on  their  magnitude  and  the  lever  arm  through  which  they  act. 
This  system  is  best  adapted  to  show  moving  vehicles  running 
over  smooth  pavements,  such  as  the  light  electric  vehicles  in 
common  use. 

Between  the  limits  of  reversible  and  irreversible  steering 
gears,  is  the  semi-reversible  type,  which  allows  the  vehicle  wheels 
to  be  turned  independently  of  any  effort  exerted  on  the  steering 
wheel,  yet  exerting  an  even  resistance  to  movement.  This  feature 
allows  the  road  wheels  to  follow  the  path  of  least  resistance  and 
at  the  same  time  indicates  to  the  operator  the  extent  and  direc- 
tion of  the  movement  by  more  or  less  swerving  of  the  steering 
wheel  depending  upon  the  gear  ratio.  The  semi-reversible  sys- 
tem also  relieves  the  parts  of  considerable  strain  which  would  be 
present  if  the  vehicle  wheels  wrere  rigidly  held  to  their  position. 
A  disadvantage  of  the  semi-reversible  feature  is  in  steering 
through  sandy  or  muddy  roads  and  in  crossing  obstructions  such 
as  car  tracks  obliquely. 

Irreversible  Gear  for  Heavy  Service, — Heavy  service  seems  to 
offer  a  logical  field  for  the  irreversible  gear  as  the  connection 
may  be  made  heavy  and  strong.  Considerable  manipulation  of 
the  steering  wheel  is  usually  necessary  on  these  vehicles,  which 
tends  to  make  this  type  a  favorite  by  relieving  the  operator  of 


STEEEING  GEARS  197 

jerks  and  considerable  muscular  exertion  on  the  steering  wheel. 
It  also  permits  a  very  low  gear  ratio  or  large  hand  wheel  motion 
which  is  quite  desirable  from  the  leverage  standpoint  in  operating 
a  heavy  vehicle  when  at  a  standstill  or  moving  very  slowly. 

Steering-gear  Ratios. — Because  a  commercial  vehicle  is  heavier 
and  slower  than  a  pleasure  car,  it  necessarily  has  a  different  kind 
of  steering  gear.  Theoretically  the  layout  would  be  the  same  for 
both  machines,  if  they  had  the  same  wheelbase,  but  practically  it 
is  necessary  to  have  a  greater  reduction  in  the  commercial  vehicle 
because  it  is  heavier  and  naturally  takes  a  greater  leverage  to 
turn  the  wheels;  and  also,  since  this  vehicle  acts  at  a  slower  rate 
of  speed,  the  reduction  can  again  be  greater  because  it  is  not  so 
necessary  to  be  able  to  turn  the  wheels  from  one  side  to  another 
quickly. 

Owing  to  the  great  inertia  of  a  moving  loaded  commercial 
vehicle,  it  is  not  desirable  to  make  quick  turns  with  the  front 
wheels  on  account  of  the  tremendous  stresses  involved  by  the  in- 
ertia force  and  the  high  center  of  gravity. 

The  term,  irreversible,  in  itself,  is  confusing  because  it  has 
no  exact  meaning  when  applied  to  a  steering  gear,  beyond  the 
rather  indefinite  condition,  that  it  means  that  any  ordinary  road 
wheel  impact  will  be  insufficient  to  turn  the  steering  wheel.  It  is 
simply  a  question  of  reduction  between  the  worm  and  gear  or 
screw  and  nut,  whichever  system  is  used.  The  greater  the  reduc- 
tion the  less  reversible  the  system  and  likewise  the  slower  the 
motion  of  the  road  wheels  in  relation  to  the  movement  of  the 
steering  wheel.  Hence,  the  steering  mechanism  for  a  heavy 
vehicle  will  be  less  reversible  than  the  steering  mechanism  for  a 
lighter  vehicle. 

Tie  Rod. — The  tie  rod  connects  the  steering  knuckle  levers  on 
opposite  sides  and  is  usually  of  tubular  section.  When  placed  in 
front  of  the  axle  it  ordinarily  works  under  tension,  while  behind 
the  axle  it  works  under  compression.  In  the  forward  position 
the  road  resistance  encountered  by  the  front  wheels,  acting 
through  the  steering  knuckles  and  arms,  puts  a  tension  on  the  rod 
and  in  the  rear  position  a  compression.  The  force  impressed  by 
the  operator  in  steering  the  vehicle  produces  a  tension  for  one 
direction  of  motion  and  a  compression  for  the  other,  with  both 
constructions. 

The  ends  of  the  knuckle  levers  swing  in  the  same  plane  and 
the  tie  rod  must  be  connected  with  forked  connectors.  These 


198    MOTOK  TEUCK  DESIGN  AND  CONSTRUCTION 


connectors  are  generally  made  adjustable,  so  that  the  wheels  may 
be  kept  properly  lined  up  even  if  the  rod  or  steering  levers  be- 
come slightly  bent.  The  adjustable  connectors  must  be  securely 
clamped  and  safeguarded  against  working  loose. 

The  Drag  Link. — The  drag  link  may  be  placed  either  in  a  fore- 
and-aft  position  or  crosswise  of  the  vehicle.  The  fore-and-aft 
position  is  more  generally  used  when  the  engine  is  under  a  hood, 
while  with  the  seat  over  the  engine  it  is  difficult  to  place  the  gear 
in  such  a  position  as  to  permit  placing  the  drag  link  parallel  with 
the  frame.  The  gear  usually  is  so  close  to  the  front  axle  that  the 
drag  link  must  be  placed  crosswise. 

Cushion  springs  are  usually  put  in  the  joints  of  this  member 
to  assist  in  absorbing  abrupt  shocks  which  might  be  transmitted 
in  either  direction.  These  members  sometimes  are  made  adjust- 
able for  length,  while  ad- 
justments are  also  provided 
to  take  up  the  tension  on 
the  springs. 

An  important  point  in 
the  steering  gear  layout  is  a 
desirability  of  a  proper  ge- 
ometrical layout  for  the 
drag  link  to  avoid  front 
wheel  Avobble  under  front 
spring  deflection  when  the 
vehicle  is  in  motion.  In 
other  words,  it  is  very  im- 
portant to  have  the  drag 
^  ,  „  .  ,  link  so  arranged  as  to 

FIG.   172.     Steering-  Gear  Back  of  Axle 

and  Drag  Link  Parallel  with  Frame,      produce  the  least  tendency 

to  rotate  the  steering  gear 

arm  as  a  result  of  the  action  of  the  front  springs.  When 
this  member  is  placed  crosswise  it  should  be  in  nearly  the 
same  plane  as  the  tie  rod  under  normal  load,  but  with  the  fore- 
and-aft  position  conditions  are  entirely  different.  With  this 
arrangement  the  drag  link  may  be  either  forward  of  or  behind 
the  front  axle.  In  the  latter  position,  which  is  the  more  popular, 
this  link  should  be  so  placed  that  when  the  truck  is  loaded,  a 
straight  line  drawn  through  the  eye  of  the  front  spring  will  ap- 
proximately intersect  both  front  and  rear  ball- joint  centers  of 
the  drag  link,  as  in  Fig.  172.  A  slight  deviation  from  this  inter- 


STEERING  GEARS 


199 


section  will  not  materially  affect  the  results,  depending  upon  the 
characteristics  of  the  front  spring,  but  the  centers  must  fall  ap- 
proximately on  this  line  to  obtain  the  proper  front  wheel  action 
under  spring  deflections,  particularly  when  such  spring  deflection 
is  at  all  excessive.  To  give  as  nearly  as  possible  true  steering 
under  extreme  conditions,  it  is  well  to  make  the  front  spring  as 
flat  as  possible,  to  prevent 
any  great  extent  of  forward 
or  backward  movement  of 
the  axle. 

On  the  Mack  model  "A.C." 
trucks  (Fig.  173)  the  steer- 
ing gear  and  drag  link  are 
ahead  of  the  front  axle.  This 
member  is  slightly  out  of 
parallel  with  the  frame,  when 
the  mechanism  is  in  midpo-  FIQ 
sition,  but  swings  into  posi- 
tion more  nearly  parallel 

when  the  road  wheels  are  turned.  The  front  axle,  in  its  move- 
ments, due  to  road  inequalities,  swings  through  an  approximate 
arc  about  a  point  P.  The  ball  on  the  steering  knuckle-arm  is  as 
close  to  this  point  as  conditions  permit.  The  drag  link,  extending 
backward,  swings  about  a  center  Z.  Thus,  both  the  axle  itself 
and  the  ball  on  the  steering  knuckle-arm  swing  through  approxi- 


Mack  Model   "AC" 
Gear  Arrangement. 


Steering 


FIG.  174.     Manly  Front   Spring  Mounting. 

mately  concentric  arcs  and  no  backward  or  forward  motion  is 
imparted  to  the  steering  gear  arm  due  to  spring  deflection. 


200    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

On  the  Manly  trucks  a  similar  arrangement  is  used ;  however, 
this  is  just  the  reverse  to  that  of  the  Mack  trucks,  in  that,  the 
front  end  of  the  spring  is  shackled  and  the  rear  end  rigidly  at- 
tached to  the  frame.  By  this  method  the  end  of  the  drag  link, 
which  is  pivoted  on  the  steering  gear  arm,  is  brought  very  nearly 
in  line  with  the  pivoted  end  of  the  spring  so  that  the  axle  and  the 
forward  end  of  the  drag  link  connected  with  the  axle  is  allowed 
to  travel  in  practically  the  same  curved  path. 

The  Steering  Gear. — Horse-drawn  vehicles  are  ordinarily 
steered  by  means  of  a  fifth-wheel  attached  to  the  forward  unit  of 
the  vehicle  gear,  which  pivots  on  what  is  known  as  the  king  bolt. 
However,  the  divided  axle  is  universally  employed  on  commer- 
cial cars.  This  was  described  in  the  preceding  chapter  on  "  Front 
Axles,"  and  the  arrangement  of  pivoting  the  wheels  is  known  in 
the  country  as  the  Ackerman  Steering  Gear. 

Technically,  this  has  been  revised  and  at  present  it  is  based 
upon  the  principle  that  if  the  vehicle  is  to  turn  a  corner  without 
lateral  slip  of  any  of  the  wheels,  the  steering  linkage  must  be  so 
arranged  that  the  axles  of  all  wheels  produced  always  intersect 
a  common  vertical  line,  this  vertical  line  forming  a  momentary 
axis  of  rotation.  This  accounts  for  the  use  of  inclined  knuckle 
arms  instead  of  parallel  arms.  When  they  extend  toward  the 
rear  they  must  incline  toward  each  other  and  away  from  each 
other  when  they  extend  forward  of  the  axle.  The  inclination  is 
such  that  the  center  lines  of  the  arms  produced  meet  at  the  point 
near  the  center  of  the  rear  axle. 

Wheel  and  Mast. — Commercial  cars  are  steered  by  means  of 
hand  wheels  located  at  the  upper  end  of  the  steering  column. 
The  spider  of  the  steering  wheels  is  secured  to  a  shaft  which  gen- 
erally passes  down  through  an  outer  tube,  usually  called  the 
mast.  This  shaft  enters  a  housing  at  the  lower  end,  which  car- 
ries the  steering  mechanism  that  may  either  consist  of  a  rack  and 
pinion  bevel  pinion  and  bevel  sector,  worm  and  sector,  worm 
and  wheel,  or  screw  and  nut. 

The  steering  column  is  generally  styled  according  to  the  type 
of  steering  mechanism  employed.  One  member  of  the  mechan- 
ism has  a  shaft  extending  through  the  housing  and  carries  the 
steering  lever  which  is  connected  by  means  of  a  drag  link  to  the 
steering  arm  on  the  front  axle.  Generally  the  steering  motion  is 
geared  down  so  that  one  and  one-half  turns  of  the  hand  wheel 
will  give  the  steering  ball  arm  a  motion  of  about  60  degrees,  while 


STEERING  GEARS 


201 


the  lever  proportions  are  such  as  to  give  the  wheels  the  maximum 
angle  in  either  direction. 

For   commercial   cars,   especially   those   designed   for   heavy 
service,  it  is  considered  best  to  have  the  steering  gear  back- 


MAST 


STEERING    SHAFT 
FLOOR  BRACKET 


HOUSING 


PINION 


PINION 


RACK- 

FIG.  175.     Eack  and  Pinion  Type  of  Steering  Gear. 

locking  or  irreversible,  that  is,  so  designed  that  any  shocks  re- 
ceived by  the  road  wheels  will  not  be  transmitted  to  the  operator's 
arms.  The  lighter  vehicles  permit  the  use  of  a  slightly  reversible 
mechanism,  in  which  part  of  the  shock  is  transmitted  to  the  op- 
erator's arms,  thus  reducing  the  shocks  transmitted  to  the  steer- 
ing mechanism. 

Drag  Links  and  Tie  Rods. — Drag  links  are  usually  of  the  same 
proportions  as  the  tie  rod  of  the  axle  and  the  general  practice  is 
to  provide  cushion  springs  to  absorb  some  of  the  shock  which  is 
transmitted  to  the  steering  mechanism.  There  are  various  con- 
structions of  either  the  steering  mechanism  or  drag  link  in  use  at 


202    MOTOE  TEUCK  DESIGN  AND  CONSTEUCTION 

of  completeness,  it  will  be  necessary  to  present  some  illustra- 
tions, if  clearness  is  to  be  a  property  of  the  text. 

Rack  and  Pinion  Type. — The  rack  and  pinion  type  of  steering 
gear  (Fig.  175)  is  perhaps  the  simplest  type.  It  consists  of  a 
hollow  steering  shaft  which  carries  the  hand  wheel  at  its  upper 
end  and  a  spur  pinion  within  a  housing  at  its  lower  end.  This 
pinion  meshes  with  a  spur  rack  the  end  of  which  extends  through 


FIG.  176.     Reo  Bevel-Type  Gear. 

the  housing  and  carries  a  ball  to  which  the  drag  link  is  attached. 
The  column  has  an  outer  tube  or  mast  which  carries  a  bearing 
for  the  steering  shaft. 

This  type  of  steering  mechanism  is  only  used  for  cross  steer- 
ing and  is  completely  reversible,  so  that  the  road  shocks  are  trans- 
mitted to  the  operator's  arms.  It  is  practically  limited  to  use  on 
cars  of  1,000-lb.  capacity  and  under,  and  where  the  steering  pivots 
can  be  so  arranged  that  only  part  of  the  motion  of  the  road  wheel 
can  be  transmitted  to  the  steering  mechanism.  It  also  possesses  a 


STEERING  GEARS 


203 


disadvantage  in  that  all  the  load  is  carried  on  one  tooth,  as  the 
space  in  the  chassis  frame  is  not  large  enough  to  permit  the  pro- 
portions needed  to  have  two  or  more  teeth  in  mesh. 

Bevel-pinion  Type  (Fig.  176)  illustrates  the  bevel-pinion  and 
sector  type  of  steering  used  on  the  Reo  2-ton  chassis.  In  this 
construction  the  steering  shaft  is  made  of  solid  section,  which 
permits  securely  keying  the  hand  wheel  and  bevel  pinion  to  it. 
This,  of  course,  is  made  possible  by  placing  the  spark  and  throttle 
control  outside  of  the  steering  column  and  locating  the  levers 
below  the  hand  wheel. 

The  bevel  pinion  meshes  with  a  bevel  gear  sector  which  is 
attached  to  a  horizontal  shaft  carrying  the  steering  ball  lever. 
The  steering  motion  is  limited  by  leaving  a  portion  of  the  sector 
without  teeth,  while  the  thrust  of  the  sector  is  taken  on  a  steel 
roller,  a  spring  being  used  to  maintain  the  roller  in  contact  with 
the  sector.  A  large  bracket  forms  the  frame  attachment  and  also 


TRUNNION    BLQCK 


HU1 

STEER/ NG   LEVER 

FIG.  177.     Steering1  Gear  of  the  Fierce-Arrow  5-Ton  Truck. 

carries  the  bearings  for  the  horizontal  shaft,  the  thrust  roller  and 
supports  the  lower  end  of  the  mast. 

The  spark  and  throttle  controls,  instead  of  having  the  usual 
sector  near  the  hand  wheel,  are  controlled  by  means  of  friction 
members  and  springs,  located  below  the  foot  board  bracket,  while 
the  accelerator  pedal  is  also  mounted  on  this  bracket. 

Bevel  gear  steering  mechanisms  have  less  need  for  housings 
than  other  types,  although  in  some  cases  they  are  enclosed.  This 
type  of  gear  is  also  completely  reversible. 

Worm  and  Sector  Type  (Fig.  180)  depicts  the  worm  and  sector 
type  of  steering  used  on  the  Vulcan  5-ton  chassis.  It  has  ball- 
thrust  bearings  and  a  hollow  shaft,  however,  but  one  control, 
that  of  the  throttle  is  built  in  the  column,  the  spark  being  con- 


204    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


SPARK  CONTROL 

HAND  WHEEL 


'HRQTTLE  CONTROL. 


trolled  by  mechanism  mounted  on  the  dash.  The  lower  end  of 
the  steering  shaft  having  an  integral  worm.  This  worm  meshes 
with  a  worm-gear  sector  mounted  on  a  horizontal  shaft  and  sup- 
ported by  bushings  located  in  the  horizontal  divided  case. 

The  customary  position  for  the  steering  ball  lever  in  the  worm 
type  of  steering  gears,  is  on  the  horizontal  shaft;  however,  this 
position  generally  limits  the  motion  of  the  front  wheels  on  the 
side  on  which  the  steering  gear  is  located,  as  the  road  wheel  will 
come  in  contact  with  the  drag  link  before  it  can  touch  any  other 
part.  With  fore  and  aft  steering  the  usual  method  of  overcom- 
ing this  is  by  placing  the  steering  arm  of  the  axle  below  the  axle 
center  and  mounting  the  steering  gear  in  such  a  manner  as  to  per- 
mit the  drag  link  to 
clear  inside  the  front 
spring.  However,  this 
places  the  steering  link- 
age in  a  position  where 
it  is  practically  the  low- 
est point  of  the  vehicle 
and  very  apt  to  become 
damaged  by  striking  ob- 
stacles in  the  road.  In 
heavy  vehicles  consider- 
able clearance  is  usually 
allowed  between  the  front 
spring  and  the  frame, 
and  in  the  Vulcan  5-ton 
truck  this  clearance  is 
taken  advantage  of  to 
protect  the  steering  link- 
age, by  passing  the  steer- 
ing arm  of  the  axle 
through  this  space  so  that 
the  drag  link  comes  in- 
side the  frame.  However,  owing  to  the  limited  amount  of  space 
between  the  engine  and  the  frame,  the  steering  ball  lever  can- 
not be  mounted  on  the  horizontal  shaft  outside  of  the  housing. 
In  order  to  overcome  this,  the  worm  sector  of  the  steering  gear 
has  a  boss  which  extends  through  case  and  carries  the  lever.  In 
this  way  the  lever  is  placed  in  approximately  the  center  of  the 
column  and  has  ample  space  for  its  full  movement. 


BALL  THRUST 
SEARING 


'ADJUSTING  NUT 


STEERING  LEV  EH 


FIG.     178. 


Peerless  Steering-  Gear, 
and  Wheel  Type. 


Worm 


STEERING  GEARS 


205 


Worm  and  Wheel  Type. — The  Peerless  steering  gear  (Fig. 
178)  differs  somewhat  from  those  shown  above,  being  of  the  worm 
and  wheel  type  with  friction  controls  mounted  above  the  hand 
wheel.  This  hand  wheel  is  attached  to  the  steering  shaft  by 
means  of  a  taper  and  key,  while  the  former  is  made  large  enough 
to  form  both  the  shaft  and  the  mast. 

With  inside  controls  and  a  mast,  there  is  considerable  dif- 
ficulty in  providing  a  shaft  of  proper  proportions,  so  that  in 
eliminating  the  mast,  the  shaft  can  be  made  ample  in  size.  Al- 
though it  is  somewhat  more  difficult  to  provide  a  bracket  on  the 
foot  boards,  owing  to  the  shaft  turning  with  the  hand  wheel. 

In  this  construction 
a  complete  worm  wheel 
is  used  instead  of  a 
sector,  and  as  only 
about  90  degrees  of 
the  worm  wheel  comes 
in  contact  with  the 
worm  teeth,  while  the 
wheels  are  moved  their 
entire  turning  range, 
and  as  the  shaft  is 
squared,  the  steering  arm 
can  be  removed  and  the 
wear  taken  up  by  turn- 
ing the  wheel  through 
an  angle  of  90  degrees, 
and  another  quarter  sec- 
tion brought  into  action. 
The  thrust  is  taken  on 
ball  bearings  in  either 
direction.  The  controls 
consist  of  a  stationary 
tube  on  top  of  which  is 
mounted  a  cylindrical 
box,  with  a  horizontal 
slot  in  one  side  through 
which  the  control  levers 


STEERING 

WHEEL. 

LEVER 


LEATHER  BOOT 
LL  SOCKET 
PRING 


BALL  ON  STEERING  ARM  OF  AXLE 


FIG.  179.     Natco  Steering  Column. 


extend.  Each  control  lever  has  an  extension,  which  carries  a 
friction  segment,  being  pressed  against  the  inner  wall  of  the 
C3^1indrical  housing  by  a  spring.  The  lower  end  of  this  stationary 
tube  is  rigidly  attached  to  the  housing  so  that  it  cannot  rotate. 


206    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

A  shaft  and  tube  pass  through  the  former  to  which  the  upper  and 
lower  levers  are  attached. 

The  Natco  steering  gear  (Fig.  179)  is  also  of  the  worm  and 
wheel  type  with  suitable  ball  bearings  to  take  the  thrust  of  the 
worm,  while  a  thrust  button  takes  care  of  the  wheel  thrust.  The 
housing  is  made  in  one  piece  with  openings  for  introducing  the 
worm  and  wheel.  In  this  construction  the  steering  shaft  is  also 
used  as  the  mast;  however,  the  wheel  is  attached  to  the  shaft  by 
bolts  and  flanges.  But  one  control  is  provided,  with  the  lever 
located  above  the  hand  wheel;  however,  instead  of  passing  the 
control  shaft  through  the  case,  the  movement  of  the  control  lever 
is  transmitted  externally  by  means  of  a  double  thread  screw  or 
cam.  The  steering  shaft  has  slots  on  opposite  sides  directly  above 


FIG.  180.     Vulcan  Steering  Gear.     Worm  and  Sector  Type. 

the  housing.  These  are  enclosed  by  a  collar  which  fits  over  the 
steering  shaft  and  carries  two  dowel  pointed  screws,  which  set  in 
threads  of  the  cam.  A  fork  rests  on  this  collar  and  any  move- 
ment of  the  control  lever  will  tend  to  raise  or  lower  this  collar, 
carrying  with  it  the  fork  which  is  connected  to  the  carburetor. 

Screw  and  Nut  Type  (Fig.  177)  illustrates  a  screw  and  nut 
type  of  steering  used  on  the  Pierce  5-ton  chassis.  The  solid 
steering  shaft  has  the  hand  wheel  keyed  to  its  upper  end  and  a 
multiple  square  threaded  screw  at  its  lower  end.  This  screw 
actuates  a  nut  with  trunnions  on  its  outside  which  carry  die  cast 
trunnion  blocks  that  slide  within  the  jaws  of  a  forked  lever, 
keyed  to  the  steering  ball  lever  shaft.  The  housing  is  divided 
horizontally  and  carries  suitable  ball  thrust  bearings,  which  are 


STEERING  GEARS 


207 


adjustable  from  the  lower  end  of  the  housing.  The  spark  and 
throttle  controls  are  of  the  ratchet  and  sector  type  mounted  out- 
side of  the  column  on  the  steering  column  mast. 

Another  screw  and  nut  type  of  steering  gear  which  is  used  on 
a  number  of  trucks  is  the  Ross,  shown  in  Fig.  181.    The  hollow 


FIG.  181.     Ross  Screw  and  Nut  Type  Steering  Gear  for  Fore  and  Aft 

Steering. 

steering  shaft  carries  a  steel  screw  at  its  lower  end  mounted  be- 
tween two  ball  bearings  to  take  up  its  end  thrust.  This  screw  is 
held  to  the  shaft  by  means  of  a  brazed  joint  and  when  the  hand 
wheel  is  turned  a  steel  block  or  sleeve  is  given  later  movement. 
This  steel  block  or  sleeve  has  a  square  external  section  and  thereby 
is  prevented  from  turning  by  the  housing.  On  each  side  of  the 


208    MOTOE  TKUCK  DESIGN  AND  CONSTEUCTION 

lower  end  of  this  sleeve,  cylindrical  recesses  are  turned,  and  cylin- 
ders, which  are  free  to  rotate,  are  placed  in  these  recesses.  The 

cylinders  have  slots 
milled  in  them  which 
receive  the  projecting 
arms  of  the  steering  ball 
lever  shaft. 

The  control  levers 
are  mounted  above  the 
wheel  and  their  shafts 
pass  through  the  steer- 
ing shaft.  The  motion 
of  these  levers  is  reduced 
at  the  lower  end  by 
means  of  bevel  gears. 

Cross  Steering.— All 
of  the  gears  depicted 
above  are  best  adapted 
to  fore  and  aft  steer- 
ing, although  they  may 
in  some  cases  be  arranged 
for  cross  steering.  Fig. 
182  illustrates  the  Boss 
screw  type  of  gear,  es- 
FIG.  182.  Eoss  Screw  and  Nut  Type  Steer-  pecially  designed  for 
ing  Gear  for  Cross  Steering.  cross  .steering  on  heavy 

vehicles.    The  lower  end 

of  the  steering  shaft  is  integral  with  a  steel  screw,  which,  when 
turned  by  the  hand  wheel,  gives  a  bronze  sleeve  longitudinal 
motion.  This  bronze  sleeve  is  threaded  internally  to  receive  the 
steel  screw  and  has  spirals  milled  upon  its  external  surface.  The 
housing  has  spirals  cut  on  its  internal  surface  which  engage 
with  the  spirals  on  the  sleeve.  The  bronze  sleeve  in  addition  to 
internal  threads  contains  a  number  of  straight  key-ways.  The 
steering  ball  lever  which  projects  half  way  up  into  the  sleeve  has 
integral  keys,  so  that  when  the  sleeve  is  given  rotative  and  lon- 
gitudinal motion,  it  rotates  the  ball  lever.  The  gear  is  provided 
with  ball-thrust  bearings  and  an  adjustment  to  take  up  wear, 
and  can  be  made  semi-irreversible  or  irreversible,  depending  upon 
the  ratio  of  the  threads. 


STEEKING  GEARS 


209 


Drag  Links. — In  Fig.  179  is  shown  a  type  of  drag  link  used 
on  vehicles  up  to  about  two  tons  capacity.  It  has  ball  sockets 
which  fit  over  the  ball  on  the  steering  arm  of  the  axle.  One  of 
the  ball  sockets  is  brazed  or  welded  to  the  drag-link  tube  and  has 
an  opening  to  receive  another  socket,  which  is  retained  by  a  nut 
or  cap.  The  steering  gear  end  has  a  housing  attached  to  the  tube 
which  carries  ball  sockets  and  springs.  These  springs  are  intro- 
duced in  the  drag  link  to  reduce  the  shock.  The  ball  end  may  be 
introduced  through  holes  in  the  housing  and  sockets  or  through 
slots  which  extend  to  the  end  of  the  housing. 


FIG.  183.     Vulcan  Drag  Link. 

The  Vulcan  drag  link  (Fig.  183)  offers  an  example  of  the 
type  used  on  heavy  vehicles.  This  consists  of  a  link  of  solid 
section  threaded  on  both  ends  into  housings  which  are  divided 
on  the  ball  center.  The  ball  sockets  on  both  ends  are  provided 
with  cushion  springs,  while  the  caps  of  the  housings  are  retained 
by  long  studs.  This  tends  to  facilitate  assembling  especially 
when  the  springs  are  heavy. 

Some  makers  enclose  these  joints  in  leather  boots,  as  shown 
in  Fig.  179,  to  hold  grease  and  prevent  dirt  and  grit  from  cutting 
the  ball  surface. 

As  mentioned  previously,  universal  joints  are  necessary  at 
both  ends  of  the  drag  link,  because  the  steering  arm  moves  in  a 
vertical  plane,  and  the  knuckle  arm  in  a  horizontal  plane,  but  in- 
stead of  the  ball  and  socket  joints,  forked  joints  are  sometimes 
used.  This  type  of  joint  was  illustrated  in  the  preceding  chap- 
ter. They  are  somewhat  simpler  in  construction  and  present 
larger  bearing  surfaces.  However,  they  are  more  difficult  to  en- 
close and  cannot  take  up  wear  automatically. 


15 


CHAPTER   XV 
MOTOR  TRUCK  FRAMES 

THE  chassis  frame  practically  forms  the  foundation  of  a  com- 
mercial car,  since  all  the  power-transmitting  and  other  units  are 
attached  to  it.  It  is  often  referred  to  as  the  backbone  of  a  com- 
mercial car.  Its  construction  depends  to  some  extent  upon  the 
general  scheme  of  the  chassis  layout,  the  construction  of  power- 
transmitting  units  and  their  mounting,  as  well  as  the  method  of 
final  drive,  wheel  base,  etc. 

When  the  commercial  car  was  first  introduced,  comparatively 
little  attention  was  paid  to  the  frame,  as  other  things  such  as  the 
power  plant,  axles,  etc.,  were  deemed  of  greater  importance, 
hence  the  frame  received  slight  consideration.  However,  after 
experiencing  considerable  difficulty,  due  to  accidents  and  other 
failures  which  were  traced  directly  to  poor  frame  construction, 
commercial  car  builders  discovered  that  frames  could  be  designed 
with  greater  strength  and  with  less  weight  if  the  problem  was 
given  proper  consideration. 

Unit  Power  Plants  and  Flexible  Mounting. — The  constant 
trend  of  obtaining  perfect  alignment  for  the  engine,  clutch  and 
transmission  has  resulted  in  the  adoption  of  the  unit  power  plant 
on  some  models,  while  in  others,  particularly,  of  the  heavier  type, 
flexible  mounting  of  the  units  has  been  resorted  to.  In  fact,  re- 
gardless of  unit  construction,  all  individual  units  are  generally 
flexibly  mounted  to  some  degree,  in  order  to  relieve  them  of  the 
heavy  stresses  due  to  frame  weaving  when  the  road  wheels  mount 
an  obstacle  on  the  road  surface.  However,  since  this  subject  of 
power  plant  mountings  is  of  considerable  importance,  this  will 
be  discussed  in  detail  in  the  succeeding  chapter,  the  author  con- 
fining this  chapter  to  the  construction  of  the  frame.  In  discussing 
this  subject,  it  may  be  necessary  in  some  cases  to  refer  to  the  gen- 
eral chassis  construction  in  order  to  clearly  depict  each  type. 

The  most  prominent  types  of  truck  frames  may  be  divided 
into  three  classes,  according  to  their  popularity :  ( 1 )  The  pressed 
steel  frame,  (2)  the  structural  channel  frame,  (3)  the  structural 
I-beam  frame.  These  may  again  be  divided  into  various  classes, 

210 


MOTOR  TRUCK  FRAMES          211 

depending  upon  the  general  construction  and  material  as  well  as 
the  distribution  of  the  main  units. 

The  Pressed-steel  Frame. — The  pressed-steel  frame  is  quite 
popular  on  all  types  of  vehicles  and  is  now  universally  used  on 
vehicles  up  to  and  including  those  of  5-ton  capacity.  Structural 
channel  and  I-beam  frames  are  still  used  by  a  number  of  makers ; 
however,  the  pressed  steel  frame  is  rapidly  gaining  favor  and 
from  present  indications  will  eventually  replace  the  other  types. 

In  discussing  the  advantages  and  disadvantages  of  the  various 
types,  the  pressed  steel  frame  may  be  mentioned  as  being  lightest 
in  weight  for  equal  strength  of  the  structural  or  rolled  channel 
and  I-beam  section,  while  its  cost  is  somewhat  higher,  due  to  the 
use  of  heat  treated  material  to  obtain  maximum  strength.  The 
cost  varies  with  the  section,  material  and  the  nature  and  extent  of 
bending. 

The  straight  side  rail  is  of  course  the  cheapest  construction; 
however,  when  conditions  permit,  this  is  usually  tapered  at  the 
front  and  the  rear  and  the  forward  end  is  sometimes  formed  to 
receive  the  spring  hanger.  When  the  seat  is  placed  above  the 
engine  this  taper  is  usually  very  short,  permitting  the  paying 
load  to  be  carried  well  to  the  front.  Bumpers  are  sometimes  pro- 
vided to  protect  the  chassis,  these  may  either  be  formed  integral 
with  the  frame  or  attached  to  it  by  castings. 

When  the  side  members  are  inswept  to  permit  a  short  turning 
radius,  it  is  necessary  to  make  the  flanges  of  the  side  rail  of  con- 
siderable width  at  this  point,  tapering  gradually  toward  the  rear, 
to  provide  the  proper  strength  at  the  point  of  offset. 

Cross  Members. — Cross  members  are  usually  made  of  the  same 
material  as  the  side  rails  and  when  pressed  have  integral  gussets, 
this,  of  course,  is  not  possible  with  the  rolled  sections  so  that  the 
separate  gusset  plates  must  be  used,  thus  placing  the  strain  on 
the  rivets,  instead 'of  on  the  cross  member. 

These  frames  of  either  type  are  used  in  both  flexible  and  rigid 
constructions.  While  both  kinds  of  material  are  subject  to  heat 
treatment,  it  is  generally  conceded  that  pressed  steel  is  a  higher- 
grade  metal  than  rolled  stock.  Owing  to  its  temper  it  will  stand 
a  certain  amount  of  bending  which  would  give  rolled  stock  a 
permanent  set  or  crack  it.  It  is  alleged  that  pressed  steel  is  more 
sensible  to  vibration,  in  that  it  will  crystallize  sooner  than  rolled 
steel  under  similar  conditions.  Instead  of  being  built  up  rigid, 
as  are  rolled-steel  frames,  the  pressed-steel  frame  may  be  built  up 


212    MOTOE  TKUCK  DESIGN  AND  CONSTEUCTION 

flexible,  so  that  instead  of  taking  the  vibration  dead,  as  well  as 
sudden  shocks,  it  gives  to  them  and  transmits  them  to  other* parts, 
so  that  the  individual  vibrations  in  any  part  are  reduced  by  dis- 
tribution. The  pressed  steed  flexible  frame  may  also  be  made 
lighter  for  its  strength  because  of  its  flexibility. 

The  Rigid  Frame. — The  rigid  frame,  too,  has  advantages, 
whether  it  is  of  pressed  steel  or  rolled  stock.  It  permits  the  body 
to  be  secured  rigidly  to  it  and  as  it  does  not  give  to  the  inequali- 
ties of  the  road,  there  is  no  racking  of  the  body.  An  advantage 
of  rolled  stock  is  its  cheapness,  except  of  course  in  the  lighter 
models  of  the  assembled  type  for  which  frames  can  be  purchased 
at  low  figures.  Another  advantage  of  rolled  stock  is  the  ease 
with  which  the  wheelbase  can  be  altered.  The  maker  using  this 
type  of  frame  may  with  little  additional  expense  give  customers 
a  shorter  or  longer  frame  than  standard. 

It  is  possible  to  alter  the  pressed-steel  frame  in  length  by  cut- 
ting off  from  the  maximum  length,  although  this  disturbs  the 
nice  proportioning  of  the  frame  for  stresses,  one  of  the  important 
advantages  of  this  type. 

Effect  on  Springs. — The  effect  of  frame  construction  upon  the 
design  and  duty  of  the  springs  must  also  be  considered.  This 
feature  is  not  generally  understood,  but  has  an  important  bearing 


^m  YT--  •' 

vrvr-i-.-                             '    '                    **•     ^^ 

\ 

• 

*  \^ct/ss£rr 

\ 

i 

—  vs 

4^              -yr 

k-yA^i-  *<  —  *^ 

L.  tfifr  v  \                                         s^      ^fcffe- 

d 

J(f  ~^REAR  SPRING  BRACKETS.  ^~~                    T 

r^^lMT  SPRING  BRACKETS-—-** 

FIG.  184.     Vim  Del 

ivery  Car  Frame. 

upon  the  life  of  the  vehicle.  A  rigid  frame  relies  upon  the  springs 
to  allow  for  all  axle  displacement.  If  the  front  and  rear  wheels 
on  opposite  sides  be  raised  several  inches  simultaneously,  the 
frame  is  subjected  to  a  torsional  stress.  If  the  frame  is  rigid, 
springs  of  considerable  camber  must  be  employed  in  order  to 
absorb  the  shock  without  being  bent  past  the  limit  of  safety  and 


MOTOR  TRUCK  FRAMES 


213 


sufficiently  flexible  to  absorb  all  of 
the  shock  without  any  tendency 
to  lift  the  other  wheels  from  the 
ground.  For  this  reason  a  dif- 
ferent type  of  spring  is  used  on  a 
rigid  chassis  from  that  used  on 
flexible  ones. 

The  flexible  frame  when  diag- 
onally opposite  wheels  are  raised 
does  not  impose  all  of  the  duty 
on  the  springs,  but  warps  and  ab- 
sorbs a  part  of  the  stress.  For 
this  reason  springs  on  flexible 
chassis  are  usually  flat  or  nearly 
so,  with  a  reduced  amount  of  play. 
Flexible  construction  also  permits 
the  frame  to  be  carried  equally  as 
low  as  with  the  underslung  spring, 
and  yet  the  spring  is  perched 
above  the  axle,  where  it  is  more 
nearly  in  line  with  the  center  of 
gravity,  thus  reducing  sidesway. 

Details  of  construction  such  as 
spring  hangers,  etc.,  Vary  consid- 
erably, as  can  be  noted  from  the 
descriptions  of  the  various  types, 
which  follow : 

Specific  Illustrations.  —  The 
Vim  4-ton  frame  (Fig.  184)  il- 
lustrates a  construction  of  pressed 
steel,  with  straight  side  rails  and 
cast  spring  hangers  which  are 
riveted  to  the  former.  Owing  to 
its  shortness  on  account  of  the 
small  size  of  the  vehicle  this  frame 
is  unusually  strong. 

The  Reo  f-ton  frame  (Fig. 
185)  also  employs  straight-side 
rails;  however,  these  are  tapered 
and  bent  at  the  front  end  to  re- 
ceive the  spring  hanger.  This  il- 
lustration shows  in  detail  all  parts 


214    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


which  are  riveted  to  the  frame  and  also  a  rigid  sub -frame  con- 
struction, which  is  set  at  an  angle  to  provide  as  near  as  possible 
a  straight-line  drive  to  the  rear  axle.  All  cross  members  are 
provided  with  integral  gussets,  while  pressed-steel  parts  such  as 
step  hanger,  body  brackets,  etc.,  are  used  to  keep  the  weight 
within  reasonable  limits  for  this  size  of  vehicle.  One-ton  frames 
are  built  along  similar  lines. 


TRfGAL  Gusserrs 


—  DOUBLf 
CROSS  MEMBER 
TO  BRACE  FRAME 


STfiAIGHr  SIDE  BAIL 


FIG.  186.     Fremont  Mais  Pressed  Steel  Frame. 

Fig.  186  depicts  the  Fremont  Mais  1^-  to  2-ton  frame,  with 
straight-side  members,  bent  at  the  front  end  to  receive  the  spring 
brackets.  In  this  construction,  the  scheme  is  to  eliminate  unnec- 
essary cross  members,  so  that  the  frame  forms  a  flexible  construc- 
tion; however,  it  presents  an  excellent  method  of  providing 
strength  at  the  point  where  the  drive,  which  is  taken  by  the 
springs,  is  transmitted  to  the  frame.  This  is  accomplished 
by  placing  two  cross  members  together  to  form  an  I-beam 
structure. 

Fig.  187  shows  the  flexible  frame  construction,  which  is  char- 
acteristic of  all  Pierce  worm-drive  trucks.  The  side  members 
are  pressed  steel  and  taper  at  both  ends,  the  front  being  bent  to 
form  the  spring  hanger,  while  the  bumper  is  also  attached  at  this 
point.  But  two  cross  members  are  used,  as  such  parts  as  the 
spring  brackets  and  torsion  rod  support  are  used  for  this  pur- 
pose, while  the  rear  member  is  of  tubular  section.  A  brace  of 
cross  shape  serves  to  form  a  flexible  support  at  the  point  of  drive. 
In  this  construction  the  drive  is  taken  through  radius  rods  at- 
tached to  a  bracket  which  also  forms  the  spring  bracket  and  car- 
ries the  tubular  member  from  which  the  torque  arm  is  supported. 

The  Locomobile  trucks  are  also  also  worm-driven  and  are 
equipped  with  radius  rods  and  torque  arm  to  take  the  torque  and 
driving  thrust;  however,  the  frame  (Fig.  188)  is  made  of  rigid 


MOTOR  TRUCK  FRAMES 


215 


216    MOTOK  TKUCK  DESIGN  AND  CONSTRUCTION 

construction.  It  is  made  of  pressed  steel  with  side  members 
tapered  at  both  ends  and  cast  spring  brackets  riveted  to  the  side 
rails.  The  forward  cross  member  forms  a  bumper,  while  the  re- 
maining members  support  the  transmission  and  service  brake 


FIG.  189.     DeKalb  Pressed  Steel  Frame  Inswept  at  Eear. 

and  form  braces  at  the  points  of  spring  anchorage  to  the  side 
rails.  The  extreme  rigidity  of  this  construction  can  be  noted  by 
the  numbers  of  cross  members  and  the  method  of  reinforcing  the 
rail  with  an  etxra  channel  insert. 

Fig.  189  depicts  the  De  Kalb  4-ton  frame,  which  is  also  of 
pressed  steel  with  tapered  side  members.  This  frame  is  of  con- 
ventional design  with  the  exception  of  the  side  rails,  which  are 
inswept  along  side  the  rear  springs  much  the  same  as  the  con- 
ventional side  member  is  narrowed  from  the  dash  forward  to  re- 
duce the  turning  radius.  Through  this  feature  lower  body  car- 


[3h  ?-ri  r-ra 

~T  REAM 

.^CAST  STEEL  CROSS  MEMBERS  —  ~~ 

1 

Lr  1 

¥ 

f     1 

t                                tf 

( 

V 


f/fOHT  SPRING  BRACKETS' 


JACKSHAFT 

FIG.  190.     U.  S.  Structural  Channel  Frame. 

riage  is  obtained  than  would  be  possible  otherwise.  It  also  pro- 
vides ample  clearance  for  the  radius  rods,  chains  and  springs. 
The  flange  width  is  increased  at  the  point  of  offset  to  provide 
proper  strength. 


MOTOR  TRUCK  FRAMES 


217 


The  United  States  3-ton  frame  (Fig.  190)  is  an  illustration 
of  the  structural  or  rolled  channel  frame,  combined  with  steel 
castings  and  a  construction  in  which  each  unit  is  mounted  as 
flexibly^  as  possible.  The  forward  three  cross  members  are  steel 
castings,  the  fourth  of  I-beam  section  rolled  steel  and  the  rear  of 
channel  shape  rolled  steel.  The  front-spring  hangers  are  formed 
integral  with  the  front  cross  member,  which  is  in  two  halves, 
bolted  together  at  the  center. 


FIG.  191.     Knox  Tractor  Frame. 

The  Knox  tractor  frame  (Fig.  191)  is  made  from  rolled  steel 
of  channel  shape;  however,  it  is  comparatively  short,  as  the  rear 
axle  is  attached  to  the  frame  by  means  of  cantilever  rear  springs. 
Thus  the  frame  merely  extends  far  enough  to  carry  the  support 
on  which  the  spring  pivots.  The  illustration  shows  the  combined 
jackshaft  and  brake  support  bracket  and  other  parts  which  are 
riveted  to  the  frame.  Large  gusset  plates  are  used  at  the  front 
and  rear  end,  while  the  front  cross  member  extends  to  each  side 
and  is  curved  to  form  the  bumper. 

The  3-ton  Yelie  frame  (shown  in  Fig.  192)  is  built  up  from 
rolled  steel  of  I-beam  section,  with  subframe  members  of  chan- 


218    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


11 


&d 


I 


nel  section.  It  is  of  the  rigid 
type  well  braced,  and  provided 
with  heavy  gusse't  plates.  The 
front  cross  member  is  bolted  in 
position  for  easy  access  to  the 
power  plant.  Diagonal  braces  of 
channel  section  are  placed  between 
the  third  and  fourth  cross  mem- 
bers for  stiffening  the  frame.  It 
is  claimed  that  I-beam  section  pro- 
vides a  much  heavier  and  stronger 
frame,  due  to  greater  width  of  the 
flanges. 

To  eliminate  the  braking  of 
frames,  there  seems  to  be  a  gen- 
eral movement  against  drilling 
any  rivet  or  bolt  holes  in  the  bot- 
tom flanges  of  the  side  rails.  In- 
stead of  drilling  the  flanges  in 
attaching  the  body  and  frame 
brackets,  the  vertical  section  of 
the  frame  is  drilled.  There  is  less 
weakening  of  the  frame  by  this 
process.  There  is  also  a  decided 
tendency  toward  the  use  of 
straight-side  rails.  A  novel  fea- 
ture which  accomplishes  this  is 
used  on  the  Nash  trucks  and  illus- 
trated in  Fig.  193.  Instead  of 
tapering  the  frame  at  the  front 
end  as  is  usual  by  carrying  the  top 
flange  straight,  the  taper  is  accom- 
plished by  keeping  the  bottom 
flange  straight  and  tapering  the 
top  gradually  down  to  the  spring 
horn.  Bolting  instead  of  riveting 
frame  members  and  castings  is  also 
receiving  serious  consideration  at 
present. 

Structural  steel  of  channel  or 
I-beam  section  is  bought  from  the 
steel  mills  in  stock  lengths.  It  is 


MOTOR  TRUCK  FRAMES          219 

usually  manufactured  from  Bessemer  steel,  afterward  subjected 
to  open  hearth  process  in  which  it  is  saturated  with  carbon,  to 
certain  specifications  for  certain  uses. 


FIG.  193.     Nash  Frame  showing  Taper   of  Upper  Flange. 

Pressed  steel  is  purchased  in  sheet  form,  cut  to  the  proper 
shape  in  the  flat  and  then  pressed  into  channel  form  under  great 
pressure.  It  is  made  of  steel  rolled  into  sheets ;  it  is  made  some- 
what closer  grained,  and  there  is  no  breaking  of  the  flake  in  the 
rolling  operation.  The  pressed  steel  frame  permits  of  greater 
simplicity  in  assembling,  since  parts  can  be  easily  bolted  or 
riveted  to  it. 


CHAPTER  XVI 

POWER  PLANT  MOUNTINGS 

AN  interesting  problem  in  connection  with  commercial  car 
designing  which  merits  careful  consideration  is  that  of  mounting 
and  arranging  the  power  plant  so  as  to  protect  it  from  stresses 
caused  by  frame  weaving,  due  to  road  irregularities.  Vibration 
is  another  factor  of  considerable  magnitude  that  must  be  consid- 
ered, while  provision  must  also  be  made  for  torque  reaction. 

Power-plant  mounting  is  being  freely  discussed  and  there 
seems  to  be  a  general  tendency  toward  some  form  of  flexible  sup- 
port, so  that  sufficient  freedom  is  given  the  engine,  while  others 
resort  to  a  spring  mounting,  which  combined  with  a  flexible  sup- 
port, protects  the  power  plant  from  vibration  and  frame  weaving. 

Opinions  differ  greatly  as  to  the  correct  mounting,  some 
maintaining  that  the  usual  method  of  bolting  down  the  two  rear 
engine  arms  rigidly  to  the  side  rails  of  the  frame  does  not  give 
the  engine  sufficient  freedom,  even  if  a  flexible  support  is  pro- 
vided at  the  forward  end.  Others  take  the  opposite  view,  claim- 
ing that  the  front  flexible  support  is  sufficient.  There  are  also 
some  engineers  who  claim  good  results  can  be  obtained  by  a  rigid 
central  support  at  the  front  end,  as  this  practically  gives  a  three- 
point  support,  and  permits  frame  weaving  to  be  taken  up  by  the 
cross  member  which  supports  the  forward  end  of  the  engine. 

The  material  give  of  the  cross  member  should  absorb  severe 
stresses  and  also  hold  the  engine  more  rigidly  against  torque 
reaction. 

If  the  engine  is  mounted  with  a  pivoted  support  at  the  for- 
ward end,  the  torque  reaction  caused  by  an  explosion  in  the  front 
cylinder,  must  be  transmitted  through  the  crankcase  to  the  rear 
engine  arms  before  it  reaches  the  frame.  However,  if  the  for- 
ward support  is  of  the  rigid  type,  the  stress  goes  to  the  frame 
direct. 

In  addition  to  the  flexible  front  support,  some  makers  also 
provide  swivel  supports  for  the  rear  arms,  so  that  all  the  torque 
reaction  must  go  to  the  rear  arms,  but  no  frame  distortion  can  by 
any  possibility  put  a  stress  upon  the  crankcase.  Larger  and  more 
massive  engine  arms  are  also  being  used,  thus  increasing  the 
efficiency  of  the  present  mountings. 

220 


POWER  PLANT  MOUNTINGS 


221 


Coil  springs  of  considerable  strength  are  also  used  under  the 
front  or  rear  supports,  and  these  absorb  some  of  the  stress  created 
by  frame  weaving,  while  they  can  also  be  arranged  to  absorb 
some  vibration. 

An  important  point  with  a  rigid  mounting  is  the  method  of 
securing  the  rear  arms  to  the  side  rails  of  the  frame.  In  this  case, 
the  engine  must  be  held  securely,  and  the  frame  must  not  be  ap- 
preciably weakened,  while  the  arrangement  must  be  such  that  the 
supporting  arms  can  be  quickly  freed  when  it  is  desired  to  re- 
move the  engine  from  the  chassis. 

In  the  unit  power  plant  the  transmission  is  supported  from 
the  flywheel  housing,  but  in  the  amidship  position,  it  is  usually 
mounted  on  a  three-point  support,  so  that  it  has  a  certain  degree 


FIG.  194.     A  Prominent  Type  of  Flexible  Support,  which  may  be  Adapted 
to  Either  the  Engine  or  a  Unit  Power  Plant. 

of  flexibility  to  resist  frame  weaving.  In  some  cases  where  a 
flexible  subframe  is  used  for  the  motor,  this  is  also  arranged  to 
support  the  transmission.  For  midship  mounting,  cross  mem- 
bers of  the  frame  are  usually  used,  so  that  the  forward  support 
forms  the  flexible  member,  while  the  rear  carries  the  two  rigid 
supports. 

One  of  the  most  prominent  types  of  flexible  supports  is  shown 
in  Fig.  194,  which  may  be  adapted  to  either  the  engine  or  a  unit 
power  plant.  This  particular  illustration  represents  the  Globe 
1-ton  truck,  equipped  with  a  Continental  engine.  In  this  con- 
struction two  cast  arms  integral  with  the  flywheel  housing,  form 
the  two  rigid  points  of  support.  These  are  set  on  hangers,  riveted 


222    MOTOE  TKUCK  DESIGN  AND  CONSTKUCTION 

to  the  side  rails  of  the  frame,  while  bolts  pass  vertically  through 
both,  to  hold  the  power  plant  in  position. 

The  third  point  of  support  is  at  the  front  end  of  the  engine, 
and  consists  of  a  bracket  fitting  over  a  finished  surface,  on  the 
hub  extension  of  the  gear  cover  plate.  A  cross  member  passes 
under  this,  and  has  the  bracket  fastened  to  it  by  two  bolts. 


FIG.  195.     A  Three-Point  Main  Frame  Mounting  Employed  on  the  Riker 

Trucks. 

This  engine  is  also  used  on  the  Denby  trucks,  and  is  mounted 
in  a  similar  manner,  but  in  order  to  provide  more  flexible  rear 
supports,  one  bolt  on  each  side  is  fitted  snugly  and  provided  with 
a  coil  spring,  the  others  being  a  loose  fit. 

Another  type  of  three-point  mainframe  mounting  is  shown  in 
Fig.  195,  being  employed  on  the  Eiker  commercial  cars.  In  this 
construction,  a  heavy  drop  forged  member  is  attached  to  the 
crankcase  at  the  rear  by  studs,  which  pass  clear  through  the  case. 
These  studs  are  so  close  together  that  considerable  freedom  is  ob- 
tained by  this  supporting  member,  through  the  elastic  extension 
of  the  studs,  and  the  elasticity  of  the  forged  member.  The  for- 
ward end  is  also  supported  by  a  forged  member ;  however,  this  is 
pivotally  arranged  in  a  bracket  bolted  to  the  crankcase.  Metal 
filling  blocks  are  fitted  into  the  side  rails  of  the  frame,  and  three 
bolts  in  each  end  of  these  supports  secure  the  engine  to  the  frame. 
The  top  flange  of  the  supports  overhangs  the  filling  blocks,  and 
so  relieves  the  bolts  from  the  weight  of  the  engine. 

The  Pierce  5-ton  truck  engine  is  also  mounted  in  a  similar  man- 
ner, while  the  Packard  truck  engines  have  a  pivot  mounting  at 


POWER  PLANT  MOUNTINGS 


223 


the  front  end,  and  the  rear  end  is  supported  by  a  large  member 
which  is  bolted  to  the  flywheel  housing. 

An  interesting  and  simple  method  of  support  is  used  on  the 
Union  trucks  (Fig.  196),  which  is  covered  by  patent.  The  for- 
ward support  is  of  swivel  type,  consisting  of  a  bracket  fitting 
over  a  hub  extension  of  the  timing  gear  cover.  This  bracket  has 


FIG.  196.     Simple  Method  of  Support  used  on  the  Union  Trucks. 


two  lugs  which  rest  on  the  upper  flange  of  the  cross  member,  so 
that  the  weight  is  taken  off  the  bolts  that  hold  the  bracket  in 
position. 

The  rear  support  is  a  large  cast  member  bolted  to  the  flywheel 
housing,  which  has  a  trunnion  formed  on  each  side,  and  these  fit 
into  brackets,  that  in  turn  are  bolted  to  hangers  riveted  to  the 
frame  side  rails.  This  gives  the  engine  somewhat  greater  free- 
dom, and  permits  taking  the  torque  reaction  on  the  rear  member. 

The  Signal  truck  has  an  unusual  engine  mounting  (Fig.  197), 
which  is  also  covered  by  patent.  In  this  construction,  swivel  sup- 
ports are  also  used  on  the  rear  arms,  for  with  such  a  layout  the 
torque  reaction  must  all  go  to  the  rear  arms,  but  no  frame  distor- 
tion can  by  any  possibility  put  a  stress  upon  the  crank  case.  A 
bracket  developed  into  spherical  shape  is  bolted  to  the  arms  ex- 
tending from  the  flywheel  housing  and  supported  by  brackets 
bolted  to  the  frame  members.  The  forward  support  is  of  the 
pivoted  type,  similar  to  the  Riker,  having  a  drop-forged  member 
that  is  supported  by  coil  springs  and  brackets  attached  to  the 


224    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


frame  members.  A  long  stud 
supports  the  springs  above  and 
below  the  frame  brackets,  so 
that  the  springs  relieve  the  en- 
gine of  severe  shocks  and  vi- 
bration. 

The  Diamond  T-trucks  also 
have  a  swivel  rear  support  of 
the  ball-and-socket  type,  and 
the  front  support  is  of  the  piv- 
oted type,  supported  from  a 
channel  section  cross  member, 
which  is  also  used  to  support 
the  radiator. 

One  of  the  chief  difficulties 
encountered  in  combining  the 
engine  and  transmission  in  a 
single  unit  is  due  to  the  fact 
that  the  flywheel  is  located  be- 
tween them  and  to  enclose  it 
requires  a  great  deal  of  metal, 
adding  both  to  the  weight  and 
the  cost.  In  commercial  car 
practice  the  four-cylinder  en- 
gine seems  to  have  become  the 
standard  and  with  these  there  is 
a  tendency  to  use  a  flywheel  of 
inadequate  capacity,  when  it  is 
to  be  enclosed,  which  detracts 
somewhat  from  the  steady  run- 
ning qualities  of  the  vehicle. 
To  overcome  this,  two  expe- 
dients may  be  resorted  to.  One 
is  to  place  the  flywheel  at  the 
front  end  of  the  engine,  but 
there  are  a  number  of  objections 
to  this  practice.  The  purpose 
of  this  flywheel  is  to  equalize  the 
torque  of  the  engine  before  it  is 
transmitted  to  the  transmission 
and  its  logical  place  therefore 
seems  to  be  between  these  two 
units.  The  forward  location  also 


POWER  PLANT  MOUNTINGS 


225 


places  it  in  a  position  where  it  can  easily  be  injured,  while  the 
strains  on  the  tires  are  increased  and  the  clearance  between  the 
engine  and  front  axle  is  materially  reduced. 

On  the  Dorris  commercial  cars  all  the  features  of  an  open  fly- 
wheel are  retained  as  illustrated  in  Fig.  198,  by  joining  the  en- 
gine and  gear  box  by  a  large  yoke  which  permits  the  use  of  a 
large  flywheel  and  also  affects  a  considerable  saving  in  weight. 


2 a" FLY    WHEEL 


YOKE 


FIG.  198.     The  Dorris  Unit  Power  Plant. 


The  method  of  mounting  the  engine  in  the  United  States 
motor  trucks  is  illustrated  in  Fig.  199.  The  engine  is  mounted 
on  a  subframe,  the  front  cross  member  of  which  extends  into  the 
side  members  of  the  frame.  This  cross  member  has  ends  that 
form  a  yoke  into  which  are  placed  heavy  coil  springs,  retained  by 
a  long  bolt,  passing  through  a  bracket  riveted  to  the  frame,  thus 
utilizing  the  springs  to  absorb  severe  shocks  and  vibration. 

A  5-in.  spherical  bearing  riveted  to  the  rear  of  the  subframe 
forms  the  rear  support.  This  rests  on  a  large  cast  cross  member, 
which  is  dropped  considerably  at  the  center.  The  support  is  on 
the  upper  side  of  this  cross  member,  thus  providing  a  very  flex- 
ible mounting. 

The  larger  sizes  of  Kissell  Car  trucks  also  have  the  power 
plant  mounted  on  springs  at  both  ends,  with  provision  for  flex- 
16 


226    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


ible  mounting  incorporated  in  the  rear  supports  as  depicted  in 
Fig.  200.  The  engine  is  mounted  upon  a  pressed  steed  subframe 
having  cross  members  at  both  ends,  which  are  dropped  consid- 


FIG.  199.     Sub-Frame   Arrangement  used   on  the   United   States   Trucks. 

erably  at  their  center.    The  front  cross  member  has  two  pressed 
steel  brackets  which  rest  on  heavy  coiled  springs  placed  inside 


-FRONT  SUPPORT 

FIG.  200.     Kissel-Kar  Six-Ton  Sub-Frame  Mounting. 

of  the  front  cross  member  of  the  main  frame.  Another  spring  is 
placed  below  the  flange  of  this  cross  member,  a  bolt  being  used  to 
hold  both  springs  in  position.  In  this  way  the  movement  of  the 


POWER  PLANT  MOUNTINGS 


227 


MAIN   FRAME 


HINGE 


MA/M  FRAME 


forward  end  of  the  subframe  is  controlled  in  both  directions. 
The  rear  support  is  formed  by  brackets  riveted  to  the  subframe 
members,  which  have  a 

T  "I  J  "I  J  J_  ^— *        I"~ 1 

m 


ball-shaped  end  that  rest 
on  ball  sockets  placed 
within  a  bracket  riveted  to 
the  main  frame  members. 
These  ball  sockets  are  pro- 
vided with  springs,  to  re- 
lieve the  power  plant  of 
shocks  due  to  vibration 
while  the  ball  permits  a 
certain  degree  of  flexibility 
when  the  frame  twists.  In 
reality  this  is  a  four-point 
suspension  which  retains 
all  the  features  of  a  three- 
point  suspension. 

The  same  principles  of  unit  power-plant  mounting  may  be 
applied  to  vehicles  in  which  the  engine  or  both  engine  and  trans- 
mission are  carried  on  a  subframe.  Fig.  201  illustrates  this 
feature  applied  to  Mogul  trucks.  The  frame  has  a  front  cross 
member  which  carries  a  bracket  to  form  the  bearing  for  the  third 
point  of  support.  The  subframe  is  also  provided  with  a  cross 

member  and  a  bearing 
bracket,  so  that  a  hollow 
pin  can  be  inserted.  This 
is  retained  by  a  large 
nut,  having  a  hub,  which 
together  with  the  pin 


WVOT 


H/NGE 


FIG.  201.    Mogul  Power-Plant  Mounting. 


MAIN 
FRAME 


SUPPORT 


FIG.  202. 


Three-Point  Suspension  of  the 
DeKalb  Sub-Frame. 


forms  the  bearings  for 
the  starting  crank.  The 
rear  ends  of  the  sub- 
frame  being  supported 
from  a  frame  cross  member. 

A  similar  construction  (Fig.  202)  is  used  on  the  Dr.  Kalb 
commercial  cars.  However  in  this  case  the  hinge  is  placed  at  the 
front  end  of  the  subframe  members,  while  the  rear  end  has  a 
large  drum  which  forms  a  single  hinge.  Fig.  203  illustrates  a 
sectional  view  of  this  rear  support  and  also  illustrates  the  method 
of  supporting  the  front  end  of  the  transmission  from  this  point. 
The  transmission  is  bolted  to  the  jack  shaft  and  has  a  long  torque 


228    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


INGE 


tube  extended  to  this  third  point  of  support,  which  is  of  spherical 

form. 

The  principle  of  three-point  suspension  in  the  Blair  trucks 

(Fig.  204)  is  even  carried  on  to  the  rear  axle.  In  this  construc- 
tion the  subframe  is  hinged 
to  the  main  frame  in  front 
by  steel  castings  and  heavy 
hardened  and  ground  steel 
pins.  At  the  rear  it  is 
hinged  at  right  angles  to  the 
worm-drive-axle  housing.  It 

O 

is  claimed  that  this  system 
renders  the  subframe  that 
carries  the  power  plant  flex- 
ible to  any  position,  main- 
taining perfect  alignment  in  the  transmission  of  power.  It  pro- 
vides a  straight-line  drive  under  all  conditions,  and  almost  en- 
tirely eliminates  universal  joints  in  the  drive. 


3PHEft/CAL   BEARING 


FIG.  203.     DeKalb  Sub-Frame  and 
Transmission  Support. 


FIG.  204.     Sub-Frame  Arrangement  used  on  the  Blair  Trucks. 

Flexible  mountings  are  also  applied  to  transmissions  when 
these  are  located  amidship.  An  excellent  example  of  this  is  the 
United  States  mounting  (Fig.  199),  in  which  spherical  or  ball- 
and-socket  joints  are  used  at  three  points,  one  at  the  forward  end, 
and  one  at  each  side  in  the  rear  over  the  jack-shaft  housing. 


POWER  PLANT  MOUNTINGS 


229 


On  the  Packard  trucks  the  transmission  (Fig.  205)  is  sup- 
ported by  two  pressed-steel  cross  members.  The  forward  end  is 
bolted  to  a  cross  member,  which  has  a  machined  surface  that  fits 
over  the  housing,  which  supports  the  forward  or  main  shaft  of 
the  transmission.  The  rear  end  is  free  and  pivotally  mounted  in 
the  brake  anchor,  which  is  attached  to  the  cross  member. 


FIG.  205.     Method  of  Supporting-  the  Transmission  on  a  Packard  Truck. 

On  the  Federal  truck  a  modified  three-point  support  is  used. 
The  transmission  case  has  four  lugs,  two  at  each  end,  and  these 
support  the  transmission  case,  being  attached  to  two  cross  mem- 
bers. The  two  lugs  at  the  front  are  close  together,  and  prac- 
tically produce  the  same  effect  as  a  single  point. 

Three-point  support  is  also  used  on  several  other  trucks,  the 
forward  support  being  of  the  pivot  type  while  the  rear  is  either 
directly  mounted  from  a  cross  member  or  by  brackets  attached  to 
the  transmission. 

The  advisability  of  providing  a  long  life  for  the  power  plant 
will  be  endorsed  by  all  users  of  commercial  cars,  and  since  this 
feature  can  be  accomplished  with  little  added  expense,  it  would 
seem  to  be  a  step  toward  reducing  maintenance  cost.  There  are 
very  few  makers  at  present  who  do  not  provide  a  certain  degree 
of  flexibility  in  the  mounting  of  their  power  plants. 

These  few  contended  that  there  is  little  to  be  gained  through 
this  feature;  howrever,  it  is  not  to  be  denied  that  for  commercial 
cars,  this  feature  presents  several  advantages. 


CHAPTEK  XVII 

SPKINGS  AND  SPEING  SUSPENSIONS 

COMMERCIAL  car  bodies  are  mounted  upon  the  chassis  frame, 
the  latter  being  supported  on  the  axles  through  the  intermediary 
of  steel  springs.  These  springs  are  built  up  of  a  number  of 
plates  varying  in  length  and  are  used  exclusively  to  support  the 
body,  although  coil  springs  are  used  as  auxiliaries. 

The  upper  leaf  of  this  spring  usually  has  an  eye  at  each  end 
for  connection  to  spring  brackets  on  the  frame,  or  shackles.  In 
some  few  cases  the  ends  are  left  flat  and  fit  in  brackets  so  that 
the  frame  rests  directly  on  them.  The  balance  of  the  spring  con- 
sists of  a  number  of  shorter  leaves,  the  lengths  of  which  de- 
crease uniformly,  except  in  cases  when  they  are  required  to  carry 
very  heavy  loads,  in  which  the  first  two  or  three  leaves  are  of  the 
same  length.  The  various  leaves  are  held  together  by  a  center 
bolt  or  a  band. 

The  method  of  frame  connection  depends  upon  the  type  of 
spring  and  various  other  factors,  while  the  axle  connection  is 
usually  made  by  box  clips  and  a  spring  seat  on  the  axle.  This 
seat  is  sometimes  called  a  perch,  and  may  be  formed  integral,  or 
attached  to  the  axle. 

Spring  Types. — The  simplest  type  of  spring  is  the  semi-  or 
half-elliptic  type,  while  all  other  types  are  made  up  wholly  or  in 
part  of  the  former.  They  may  be  termed  combinations  of  the 
semi-elliptic  type. 

The  three-quarter-elliptic  type  consists  of  a  semi-elliptic  lower 
member  and  a  quarter-elliptic  top  member.  These  two  members 
are  joined  by  shackles  and  bolts  at  one  end.  This  type  of  spring 
is  used  on  pneumatic  tired  vehicles  only  at  present. 

The  full-elliptic  spring  consists  of  two  semi-elliptic  members 
joined  at  both  ends  by  bolts  or  shackles  and  bolts. 

The  three-quarter  platform  spring  consists  of  two  semi-elliptic 
side  members  and  one  semi-elliptic  cross  member,  the  side  mem- 
bers being  joined  to  the  cross  members  by  shackles  and  bolts. 
This  type  is  ordinarily  termed  the  platform  spring,  since  the  true 
full  platform  spring  consisting  of  two  side  and  two  cross  semi- 

230 


SPKINGS  AND  SPRING  SUSPENSIONS          231 

elliptic  members  is  not  adaptable  to  the  ordinary  chassis  con- 
struction. 

Auxiliary  springs  consist  of  a  half-elliptic  with  plain  ends. 
The  cantilever  spring  carries  the  weight  at  its  small  end  and  may 
either  be  quarter-elliptic;  in  which  the  big  end  is  secured  to  the 
frame  or  a  semi-elliptic;  in  which  case  it  has  a  pivot  support  on 
the  frame  at  or  near  its  center,  and  is  connected  to  the  rear  axle 
at  its  rear  end. 

There  are  also  various  other  combinations;  however,  they  are 
not  employed  at  present,  and  consequently  are  not  within  the 
scope  of  this  work. 

Semi-elliptic  a  Favorite. — Regardless  of  capacity,  the  semi- 
elliptic  suspension  is  a  decided  favorite.  It  is  simple,  and  if  the 
length,  width  and  other  dimensions  are  proportioned  correctly, 
nothing  better  than  the  semi -elliptic  spring  for  front  and  rear 
suspension  could  be  desired. 

The  remaining  spring  suspensions  employed  at  present  may 
be  classified  as  follows:  Semi-elliptic  front,  full-elliptic  rear; 
semi -elliptic  front  and  three-quarter-elliptic  rear;  full-elliptic 
front  and  rear;  semi-elliptic  front  and  three-quarter  platform 
rear;  full-elliptic  front  and  platform  rear. 

Another  point  worthy  of  note  is  the  substitution  of  the  true 
sweep  spring  and  the  elimination  of  the  double  sweep  spring. 
Having  a  simple  curve,  the  true  sweep  spring  is  easy  to  fit,  and 
spring  makers  recommend  them  on  this  account.  The  double 
sweep  spring  is  simple  to  mount  and  has  a  legitimate  place  on 
every  truck  as  an  auxiliary  or  overload  spring.  Comparison  of 
these  two  types  may  be  made  by  referring  to  Figs.  206  and  207, 
the  former  being  a  true  sweep  and  the  latter  a  double  sweep 
spring. 

Until  recently,  very  few  springs  were  equipped  with  bumpers ; 
however,  in  most  cases  these  are  in  the  form  of  coil  springs,  and 
on  some  vehicles  they  are  made  of  a  heavy  square  section. 

The  general  construction  of  the  various  types  can  readily  be 
understood  by  referring  to  accompanying  illustrations;  however, 
the  method  of  frame  suspension  and  axle  mounting  warrants  dis- 
cussion. 

De  Kalb  Springs. — Fig.  206  illustrates  the  De  Kalb  rear 
spring,  which  is  of  the  semi -elliptic  true  sweep  type.  These  are 
placed  outside  of  the  frame  to  permit  carrying  the  frame  low, 
and  the  main  leaf  has  an  eye  at  each  end  which  is  connected  to 


232    MOTOE  TRUCK  DESIGN  AND  CONSTRUCTION 

the  frame  by  means  of  shackles  and  bolts  through  brackets  riveted 
to  the  frame.  All  bearing  surfaces  are  provided  with  removable 
bushings  and  grease  cups.  The  leaves  are  held  together  by  means 


FIG.  206.     DeKalb  Spring  Mounted  Outside  of  Frame  and  Over  Axle. 

of  a  steel  outer  band  which  is  shrunk  over  them.  The  spring  is 
attached  to  the  axle  by  means  of  a  spring  seat  which  is  mounted 
on  the  axle  spindle  and  prevented  from  turning  by  a  set  screw. 
Box  clips  of  square  sections,  placed  at  an  angle  are  used  to  hold 
the  spring  to  its  seat.  Two  nuts  are  used  to  hold  the  spring  rigid, 
while  the  upper  ends  of  the  clips  are  held  in  position  by  a  pres- 


FIG.  207.     Mogul  Six-Ton  Rear  Spring  with  Tlain  Ends  Showing  Method 
of  Mounting  on  Axle. 

sure  block  on  the  top  of  the  spring  which  fits  snugly  over  the 
center  band. 

The  front  spring  is  of  similar  construction;  however,  the 
front  end  of  this  is  attached  directly  to  the  front  bracket,  while 
the  rear  end  is  shackled  to  its  bracket.  The  necessity  of  directly 


SPRINGS  AND  SPRING  SUSPENSIONS 


233 


connecting  the  forward  end  of  a  front  spring  to  frame  is  due  to 
the    fact    that    this    is    the 


is 

only  connection  between  the 
frame  and  the  axle,  the 
spring  being  utilized  to 
hold  the  front  axle  in  posi- 
tion. This  is  also  true  of 
the  forward  end  of  a  rear 
spring  when  the  torque  and 
driving  thrust  is  taken 
through  the  spring.  This 
feature  was  explained  in  a 
previous  chapter  on  the  final 
drive. 


SPRING  BAND 


CUP 


SPRING 


SPRING 
SEAT 


AXLE 


FIG.  208. 


Mogul  Springs. — In  Fig. 
207  is  shown  the  Mogul 
6-ton  rear  spring,  which  is 
of  the  semi-elliptic  double 
sweep  type  with  plain 
ends.  These  ends  fit  between  the  webs  of  the  frame  bracket, 
which  has  a  hardened  steel  plate  resting  on  the  spring.  In  this 
case  the  spring  seat  is  also  mounted  on  the  axle  spindle ;  however, 


Mogul  6-Ton  Front  Spring 
Mounting. 


SPRING  CLIPP 

AXLE  HOUSING 
AXLE  DRIVE  SHAFT. 
SPRING  SEAT 
SPRING  BAND 


FIG.  209.     Chase  Underslung  Spring  Shackled  at  one  End. 

in  place  of  the  usual  box  clip,  four  heavy  bolts  with  a  T-shaped 
head  are  used.  The  bolts  fit  into  grooves  formed  into  the  walls 
of  the  spring  seat  and  the  heads  of  the  bolts  fit  into  rectangular 
holes  cast  into  the  seat.  Two  flat  bars  are  used  as  a  pressure  block 


234    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

and  are  retained  by  washers  and  nuts.  The  front  spring  is  con- 
nected to  the  frame  at  the  forward  end  by  an  eye  and  a  shackle 
bolt,  while  the  rear  end  is  plain  and  rests  against  a  hardened 
plate  on  the  bracket.  The  method  of  axle  mounting  is  similar  to 
the  rear;  however,  clips  are  used  in  place  of  bolts,  while  the 
spring  seat  is  a  steel  casting,  which  fits  over  the  axle  as  shown 
in  Fig.  208.  The  clips  pass  through  holes  in  the  seat  proper 
which  coincide  with  grooves  cut  into  the  upper  flange  of  the  axle. 
Tapered  washers  and  nuts  hold  these  together. 

Chase  Springs. — On  the  Chase  worm-driven  models,  the  rear 
springs  (Fig.  209)  pass  under  instead  of  over  the  axle,  and  also 
take  both  the  torque  and  the  driving  thrust.  For  this  reason  it 
is  necessary  to  rigidly  connect  the  front  end  of  the  spring  to  the 


FIG.  210.     I.H.C.  Full-Elliptic  Front  Spring. 

frame,  while  the  rear  end  is  shackled  to  compensate  for  elonga- 
tion under  load.  Conditions  are  reversed  in  the  axle  mounting, 
as  the  pressure  block  is  placed  under  the  spring  and  the  spring 
seat  over  it.  These  are  held  together  by  clips  of  U-shape  which 
pass  over  the  axle. 

Fig.  210  depicts  the  full-elliptic  front  spring  used  on  the 
I.H.C.  1,000-lb.  vehicles.  They  are  clipped  to  both  the  frame  and 
the  axle.  This  type  of  spring  consists  of  two  semi-elliptic  mem- 
bers, one  mounted  above  the  other,  and  are  connected  at  their 
ends  by  bolts.  This  type  is  also  employed  on  the  rear  end  of 
these  vehicles;  however,  instead  of  rigidly  connecting  the  upper 


SPRINGS  AND  SPRING  SUSPENSIONS 


235 


PRESSURE 


SPFf/NG  CLIP 

FRAME 


member  to  the  frame ;  this  is  pivoted  on  a  shaft  as  shown  in  Fig. 
211.  A  bracket  is  attached  to  the  frame,  through  which  the  shaft 
passes.  The  upper  spring  seat  pivots  on  this  shaft  and  has  the 
spring  clipped  to  it  as 
shown.  The  object  of  piv- 
oting the  upper  end  of  the 
rear  spring  is  to  compen- 
sate for  the  spring  play 
since  the  only  connection 
between  the  axle  and  frame 
with  this  type  of  spring  is 
through  the  radius  rods. 

Mack  Springs.— Fig.  212 

illustrates    the    three-quar- 
ter  platform   rear   springs 
used    on    the    heavy    duty 
Mack    trucks.      The    rear 
ends  of  the  two  side  mem- 
bers are  connected  by  double  shackles  consisting  of  two  substan- 
tial U-shaped  members  which  are  hooked  together,  the  same  as 
on  numerous  horse-drawn  vehicles. 


SPRING 

EAT 


FIG.    211.      Method   of   Mounting   I.H.C. 
Full-Elliptic  Rear   Spring. 


FRAME  SIDE  MEMBER 

FRAME  CROSS  MEMBER 


FIG.  212.     Three-Quarter  Platform  Spring  used  on  Mack  Heavy-Duty 

Trucks. 

Fig.  213  illustrates  the  overload  or  auxiliary  spring  which  is 
usually  a  semi-elliptic  member  of  the  double  sweep  type.  It  is 
attached  to  a  frame  cross  member  at  the  center  and  the  ends  are 
free  so  that  they  may  make  connection  with  a  separate  spring 
when  a  predetermined  load  has  been  applied. 

On  the  International  Harvester  Company's  trucks,  auxiliary 
springs  are  provided  which  take  action  at  a  time  when  the  main 
springs  are  about  to  be  overtaxed  and  prevent  the  load  from 


236    MOTOE  TRUCK  DESIGN  AND  CONSTRUCTION 

coming  in  dead  contact  with  the  axle.  These  auxiliary  springs 
are  of  the  quarter-elliptic  type  and  are  attached  to  the  brackets 
which  take  the  driving  strain  at  the  front  end  of  the  spring.  The 

FRAME    CROSS  MEMBER 
PfVNG  CUP 
PFUNG 


FIG.  213.     Overload  Spring  with  Separate  Seat. 

rear  ends  of  these  auxiliary  springs  are  free  to  bear  on  the  pres- 
sure blocks  of  the  rear  springs.  This  construction  is  illustrated 
in  Fig.  214. 

Knox  Tractor. — The  Knox  Tractor  employs  an  unusual 
method  of  suspension,  Fig.  215,  which  combines  a  cantilever  and 
semi-elliptic  spring  at  the  rear  end  of  the  frame.  Heavy  semi- 
elliptic  springs  are  attached  to  the  rear  axle  with  long  clips  and 
carry  the  fifth  wheel  of  the  trailer.  There  is  no  connection  be- 
tween these  and  the  tractor  frame,  so  that  they  carry  the  weight 


FIG.  214.     I.  H.  C.  Quarter  Elliptic  Overload  Spring. 

of  trailer  and  load  only.  The  tractor  frame  is  mounted  on  a  can- 
tilever spring,  having  a  pivot  near  its  center  and  a  shackle  at 
the  front  end.  The  rear  end  bears  on  a  seat  clipped  to  the  rear 
axle.  This  construction  permits  a  flexible  mounting  for  the 
tractor,  and  also  the  carrying  of  very  heavy  loads  on  the  trailer. 
There  is  a  great  variety  of  methods  of  attaching  the  springs 
to  the  frame  and  rear  axle.  Several  methods  have  been  illus- 
trated above,  while  the  following  gives  an  excellent  idea  of  the 
attention  that  is  being  devoted  to  this  vital  point. 


SPKINGS  AND  SPRING  SUSPENSIONS 


237 


FIG.  215.     Knox  Tractor  Cantilever  Rear  Spring. 

Selden  Construction. — The  Selden  construction  (Fig.  216)  has 
a  heavy  pressure  block  which  is  grooved  to  take  the  U-shaped 
clips  and  carries  a  heavy  coiled  spring 
which  contacts  with  a  bracket  riveted 
to  the  frame  and  acts  as  a  check  for  ex- 
cessive deflections.  Two  of  these  coiled 
springs  are  used  one  on  each  side. 

The  Vulcan  5-ton  front  springs 
(Fig.  217)  are  mounted  on  a  seat 
forged  integral  with  the  front  axle, 
and  are  retained  by  long  studs  which 
have  a  shoulder  near  their  center  and 
by  a  drop-forged  pressure  block. 

The  Velie  3-ton  vehicles  have  a 
rear  axle  of  round  section  and  cast 
spring  seats  which  are  held  in  position  by  a  heavy  bolt  pass- 
ing through  the  axle.  The  spring  leaves  are  held  together 
by  a  center  bolt  which  passes  through  the  pressure  block.  Long 


FIG.    216.      Selden    Spring- 
Mounting1. 


238    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


SPRING. 


FIG.  217.      Method     of    Mounting 
Vulcan  Five-Ton  Springs. 


a  heavy  pressure  block,while 
the  seat  for  the  bumper  is 
also  retained  by  the  clips. 
This  construction  is  shown 
in  Fig.  221,  while  Fig.  222 
illustrates  the  spring  shack- 
les and  the  method  of  con- 
necting these  to  the  frame. 
This  shackle  is  suspended  on 
a  very  large  shaft  extending 
the  full  width  of  the  frame 
and  supported  by  brackets 
riveted  to  the  frame. 


box  clips  are  used  to  attach  the 
spring  to  its  seat,  as  shown  in 
Fig.  218. 

Peerless  Springs. — On  the 
Peerless  trucks  the  front  springs 
are  mounted  on  a  seat  forged 
integral  with  the  axle,  and  are 
retained  by  box  clips.  Fig.  219 
illustrates  this,  and  it  will  be  noted 
that  a  coil  spring  is  attached  to 
the  pressure  block  which  acts  as  a 
bumper.  Under  excessive  deflec- 
tions these  springs  strike  the  bot- 
tom flange  of  the  frame  and  ar- 
rest the  rebound  motion  of  the 
vehicle  springs. 

The  Nash  Quad  also  employs 
a  spring  bumper  which  is  made 
of  flat  metal  and  is  termed  a  vo- 
lute spring.  This  is  attached  to  a 
bracket  fastened  to  the  pressure 
block,  as  shown  in  Fig.  220. 

The  Gar  ford  worm- driven 
models  have  the  springs  mounted 
outside  the  frame  and  the  bumper 
springs,  which  are  of  square  section 
are  mounted  directly  under  the 
frame  side.  The  vehicle  springs 
are  retained  by  U-shaped  clips  and 


FIG.  218.     Velie   Three-Ton   Rear    Spring 
Mounting. 


SPRINGS  AND  SPRING  SUSPENSIONS 


239 


BUMPER 


On  the  Selden  trucks  this  shaft  is  replaced  by  a  steel  tube 

which  ties  the  brackets  together  but  the 

shackle  is  mounted  on  a  separate  stud. 
In  the  Hotchkiss  drive,  when  the 

springs  form  the  only  connection  be- 
tween the  frame  and  re'ar  axle  and  the 

drive  is  entirely  dependent  upon  the 

main  leaf  of  the  spring,  there  is  danger 

of  spring  breakage  which  will  disable 

the  vehicle.    In  order  to  overcome  this 

disadvantage  the  Fulton  and  Garford 

companies  provide  a  three -point  shackle 

at  the  front  end  of  the  spring,  as  shown 

in  Fig.  223.     This  illustrates  how  the 

main  leaf  is  supplemented  by  the  elon- 
gated eye  in  the  second  leaf  in  caring 

for  the  driving  stresses,  which  also  illustrates  the  method  of  caus- 
ing the  third  and  fourth  leaves  to 
help  to  assist  the  two  main  leaves 
in  bearing  the  load. 


FIG.  219.  Peerless  Front 
Spring  Bumper  and  In- 
tegral Spring  Seat. 


BUMPER 


Rebound  Clips, — In  most  cases 
the  vehicle  springs  are  equipped 
with  rebound  clips,  the  purpose 
of  these  may  be  explained  as  fol- 
lows :  When  the  road  wheel  strikes 
an  obstacle  in  the  road,  the  spring 
near  it  is  compressed,  whereby 
energy  is  stored  up.  Immediately 
after  the  compression  has  ceased 
the  spring  extends  again,  and  if 
the  blow  was  a  heavy  one  the  re- 
bound will  carry  the  body  far  be- 
yond its  original  position.  This 
rebound  has  a  tendency  to  curve 
the  main  leaf  of  the  spring  in 
the  reverse  direction,  and  in  order 
to  prevent  any  serious  difficulty 

it  is  necessary  to  transmit  this  shock  to  several  of  the  leaves. 

This  is  accomplished  by  the  rebound  clips  which  are  riveted  to 

the  shortest  leaf  which  they  surround  and  connected  over  the" 

main  leaf  with  a  bolt. 


FIG.  220.  Nash  Quad  Spring 
Mounting  and  Spring  Bum- 
per. 


240    MOTOE  TRUCK  DESIGN  AND  CONSTEUCTION 


PRESSURE 
BLOCK 


FIG.  221.     Method  of  Mounting   Springs  on  the  Garford  Trucks. 


FIG.  222.     Garford  Eear  Spring  Shackled  Construction. 


SPEINGS  AND  SPEING  SUSPENSIONS          241 


FIG.  223.     Fulton  Three  Point 
Front  Shackle. 


Spring  Alignment. — Although  the  clips  at  the  center  of  the 
spring  tend  to  hold  the  leaves  in  alignment,  they  alone  are  not 
sufficient,  and  in  order  to  prevent  lateral  motion  of  the  leaves 
some  other  provision  must  be 
made.  One  of  the  most  com- 
mon methods  is  to  raise  a  cen- 
tral longitudinal  rib  on  the 
main  leaves  for  a  certain  dis- 
tance as  shown  in  Fig.  209. 
The  rib  of  one  leaf  enters  the 
corresponding  gutter  on  the 
next.  Another  plan  is  to  pro- 
vide the  leaves  with  lips  at 
right  angles  as  shown  in  Fig. 
210. 

An  objectionable  feature  of 
the  center  bolt  is  that  it  mate- 
rially weakens  the  spring  and 
quite  often  spring  breakage 
can  be  traced  to  the  weakness 
through  the  center  bolt  hole. 

For  this  reason  the  center  band,  which  is  shrunk  over  the  leaves, 
is  favored  by  a  number  of  commercial  car  builders. 

It  is  inadvisable  to  arrest  abruptly  the  motion  of  a  spring 
that  is  suddenly  deflected,  and  for  this  reason  bumpers  or  check 
springs,  as  they  are  sometimes  termed,  are  used.  Under  exccessive 
deflection  these  bumpers  strike  the  lower  flange  of  the  frame  or 
brackets  riveted  to  it  for  this  purpose.  The  bumpers  are  so  pro- 
portioned that  they  yield  under  the  load,  producing  a  cushion 
effect  the  same  as  rubber  bumpers  on  pleasure  vehicles. 

Overload  Springs. — Overload  springs  may  either  be  of  the  leaf 
or  coil  type,  and  so  arranged  as  to  act  only  when  the  load  on  the 
main  springs  reaches  a  certain  amount.  Below  this  load  they  do 
not  contact  with  their  seat  or  wear  plate.  The  wear  plate  may  be 
a  separate  platform,  as  illustrated  in  Fig.  213,  or  it  may  be 
formed  integral  with  the  pressure  block.  When  coil  springs  are 
used,  they  are  made  of  square  section,  attached  either  to  a  frame 
cross  member  or  the  axle.  Two  such  springs  are  used,  one  on 
each  side. 

Spring  Clips. — The  general  desire  to  prevent  breakage  at  the 
center  is  seen  in  the  liberal  proportion  of  the  pressure  blocks  and 
spring  clips.     They  represent  the  efforts  of  the  various  makers 
17 


242    MOTOE  TEUCK  DESIGN  AND  CONSTEUCTION 

to  provide  a  rigid  connection  between  the  spring  and  the  seat. 
There  is  a  growing  tendency  to  employ  the  U-shaped  spring  clip 
which  tends  to  exert  an  equal  hold  on  each  side  of  the  spring, 
consequently  the  tension  is  equally  distributed  when  the  nuts 
are  drawn  up  tight.  They  are  made  up  of  steel  that  will  not 
easily  become  brittle  under  vibration. 

Lubrication. — In  most  cases  the  spring  eyes  are  bushed  with 
phosphor-bronze  or  steel  and  shackle  bolts  are  hardened  and 
ground.  The  object  of  the  bushing,  of  course,  is  to  provide  some 
means  to  renew  the  wearing  surface.  The  bolts  are  working  con- 


Rear  Spring  and  Shackle  Assembly.  Front  Spring  and  Shackle  Assembly. 

FIG.  224.     Wick  Oiling  System  on  the  La  France  2-Ton  Truck  Spring 

Shackles. 

tinuously  and  will  wear  out  quickly  if  they  are  allowed  to  remain 
dry.  This  lubrication  is  effected  by  grease  cups  which  communi- 
cate with  a  hole  in  the  bolt  that  permits  the  lubricant  to  reach 
the  wearing  surface. 

In  order  to  simplify  maintenance  some  makers  provide  a  wick 
oiling  system  for  the  spring  shackles  as  illustrated  in  Fig.  224. 
This  particular  illustration  depicts  the  La  France  construction, 
while  the  Fageol  and  Military  class  B  vehicles  are  also  provided 
with  similar  wick  oiling  systems.  On  the  rear  spring  shackles 
oil  reservoirs  are  cast  integral  with  the  shackles  and  wicks  are  in- 
serted through  drilled  holes  which  feed  the  oil  to  the  various 
bearings  by  capillary  attraction.  On  the  front  springs  the  frame 
bracket  carries  the  reservoir  and  a  wick  feeds  oil  to  the  upper 
pin  which  is  hollow,  thus  permitting  the  oil  to  flow  by  gravity  to 
the  lower  shackle  pin  or  bolt. 


SPKINGS  AND  SPEING  SUSPENSIONS          243 

Although  friction  between  the  spring  leaves  is  desirable  to  an 
extent,  yet  it  is  necessary  to  keep  the  leaves  lubricated  when  they 
bear  against  one  another.  This  provision  is  usually  made  by  the 
spring  maker,  and  in  most  cases  it  is  necessary  to  pry  the  leaves 
apart  and  introduce  the  lubricant  with  a  knife. 


CHAPTER  XVIII 

THE  FUEL  SUPPLY  SYSTEM 

THE  function  of  the  fuel  supply  system  of  a  commercial  car 
is  to  furnish  the  carburetor  with  an  unfailing  supply  of  gasoline 
until  the  supply  carried  is  entirely  exhausted.  This  must  be  done 
independently  of  the  grades  encountered  by  the  vehicle.  The 
gasoline  is  generally  fed  by  gravity  from  the  tank  to  the  car- 
buretor, although  one  maker  uses  pressure  feed,  while  several 
others  use  the  vacuum  system,  which  has  been  so  successful  on 
pleasure  vehicles. 

In  the  gravity  system  the  "head"  of  fuel  is  depended  upon 
to  feed  it  to  the  carburetor.  Tank  location  therefore  is  an  im- 
portant phase  of  this  system,  and  requires  the  tank  to  be  elevated 
above  the  carburetor.  With  this  system  the  tank  may  either  be 
placed  on  the  dashboard  or  under  the  driver's  seat.  In  a  pres- 
sure feed  system  the  tank  may  be  located  at  any  level  with  ref- 
erence to  the  carburetor,  since  the  fuel  is  always  under  a  prede- 
termined pressure  sufficient  to  maintain  a  constant  level  in  the 
carburetor  float  chamber.  This  pressure  may  either  be  obtained 
from  the  exhaust  or  by  a  special  air  pump. 

In  the  vacuum  system  the  suction  of  the  engine  is  used  to 
draw  gasoline  from  the  supply  tank  to  an  auxiliary  tank,  from 
which  the  gasoline  flows  by  gravity  to  the  carburetor. 

Gasoline  Tanks. — Gasoline  tanks  are  generally  made  from 
tinned  sheet  steel,  known  as  terne  plate,  and  may  either  be  pressed 
or  formed  to  shape  with  ends  and  joints  soldered  or  riveted  and 
soldered.  In  order  to  provide  the  maximum  mileage  for  a  vehicle, 
they  must  be  made  to  hold  from  twenty  to  thirty  gallons  and 
must  be  reinforced,  so  that  the  ends  are  protected  from  being 
forced  out  as  the  fuel  rushes  from  one  end  to  the  other.  These 
reinforcements  or  baffle  plates  also  serve  to  prevent  rattling  due 
to  vibration  and  sagging  at  the  center  of  the  tank.  They  are 
provided  with  holes  or  openings  so  that  the  gasoline  can  find  a 
level  in  all  compartments. 

The  filler  cap  and  outlet  are  usually  provided  with  strainers 
which  are  made  from  metal  gauze,  while  shut-off  cocks  are  pro- 
vided in  the  outlet  to  shut  off  the  supply.  Some  makers  also 

244 


THE  FUEL  SUPPLY  SYSTEM 


245 


provide  a  reserve  supply  in  the  tank.  This  is  usually  accom- 
plished by  a  three-way  cock  fitted  with  a  stand  pipe  which 
projects  several  inches  above  the  bottom  of  the  tank.  Ordinarily 
the  gasoline  passes  through  this  stand  pipe,  but  when  the  lock 


FIG.  225.     Nash  Quad  Gasolene  Tank  and  Gravity  Feed  System. 

is  turned  to  the  reverse  position,  the  fuel  is  permitted  to  pass 
through  another  opening  flush  with  the  bottom  of  the  tank. 
These  features  are  shown  in  the  following  illustrations. 

Nash  Quad. — Fig.  225  illustrates  the  Nash  Quad  gasoline  tank 
and  the  feed  pipe  and  carburetor.  This  also  serves  to  illustrate 
the  conventional  gravity  feed  system.  The  filler  cap  is  located 


/HANDLE. 


HAfJDLE^ 
FILLER  CAP^ 


\5TRAIN  E.R 

-BAFFLE  PLA  TE  

STRAINER 

3 

^,,+ert*  ;t 

SEATSUPPOPT         0 

0 

1                     0                     0                     0                     00 

|o 

rfv, 

FRAME  1 

1 

{^^>     -* 

fr\          U 

f 

O       0        Oj 


FIG.  226.     Riker  Gasolene  Tank  and  Mounting. 

near  the  center  of  the  tank  and  is  provided  with  a  large  handle 
so  that  it  can  easily  be  removed.  A  large  strainer  fits  inside  of 
the  filler  flange,  which  is  riveted  and  soldered  to  the  tank.  The 
body  of  the  tank  is  of  rectangular  shape  and  formed  from  a  sheet' 


246    MOTOE  TEUCK  DESIGN  AND  CONSTEUCTION 

of  steel.  The  head  is  set  in  lapped  and  soldered  as  shown  in  the 
small  sectional  view.  Two  outlets  with  shut-off  cocks  are  pro- 
vided, so  that  gasoline  may  flow  from  either  or  both  ends.  Each 
of  these  cocks  are  provided  with  two  openings  level  with  the 
bottom  of  the  tank  for  the  reserve  supply,  while  the  regular 
supply  is  taken  through  the  stand  pipes. 

Fig.  226  shows  the  Eiker  tank  and  mounting.  This  tank  is 
of  the  bolster  type,  or  modified  rectangular  shape  and  provided 
with  two  baffle  plates  for  reinforcements.  The  heads  are  dished 
outward  and  the  edges  of  the  body  are  flanged  over  them  and 
soldered.  Both  filler  and  outlet  are  provided  with  strainers,  and 
two  handles  are  soldered  to  the  top  of  the  tank  so  that  it  can 
easily  be  removed  for  repairs.  The  upper  views  show  the  method 
of  mounting  the  tank  in  a  steel  compartment  which  supports  the 
driver's  seat.  This  compartment  is  made  of  sheet  steel  and  a 
framework  of  small  angles  riveted  together.  Angles  on  the  front 
and  rear  near  the  bottom  support  brackets  which  carry  the  tank. 
A  strip  .of  felt  is  placed  between  the  brackets  and  the  tank  to 
form  a  cushion  and  steel  straps  hold  the  tank  in  position. 


SEAT  SUPPORT 


FILLER  CAP 


FOOT  BOARD  SUPPORT 


-FRAME  CROSS  MEMBER 


FIG.  227.     Peerless  Gasolene  Tank  Support. 

Peerless  and  Fierce-Arrow. — Fig.  227  depicts  the  Peerless 
mounting.  However,  this  differs  from  the  above  in  that  the 
tank,  which  is  of  cylindrical  form,  is  supported  and  retained  by 
steel  straps.  It  is  carried  in  a  steel  compartment  supporting  the 
driver's  seat. 

The  Pierce  tank  is  of  rectangular  shape  and  supported  from 
the  frame  by  means  of  sheet  steel  brackets  and  wood  blocks  as 


THE  FUEL  SUPPLY  SYSTEM 


247 


shown  in  Fig.  228.     This  mounting  is  so  constructed  that  the 
framework  which  supports  the  seat  surrounds  the  tank.     A  re- 


WOOD 
BLOCK 


^T 

0 
_Q_ 


STEEL  STRAP 


PRIMING  PUMP 


FIG.  228.     Fierce-Arrow  Gasolene  Tank  and  Mounting. 

serve  compartment  is  provided  and  arranged,  accessible  through 
a  handle  outside  of  the  seat  compartment.  Gasoline  feed  to  the 
carburetor  is  by  gravity  and  a  connection  is  also  made  for  prim- 
ing the  engine  in  cold  weather.  A  hand-operated  priming  pump 


STEEL  PLATE- 
FIG.  229.     Kelley-Springfield  Gasolene  Tank  Mounting. 

is  attached  to  the  seat  compartment  and  supplies  a  small  quan- 
tity of  gasoline  to  the  motor  through  the  intake  manifold. 

On  the  Kelly  trucks  the  seat  compartment  is  also  made  of 


248    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

wood  and  the  rectangular-shaped  gasoline  tank  fits  snugly  in 
this.  It  is  supported  by  wood  beams  at  each  end  and  at  the  cen- 
ter. The  tank  is  placed  well  above  the  carburetor  to  provide  the 
proper^  head  as  shown  in  Fig.  229.  It  is  retained  by  wood  strips 
and  protected  from  excessive  heat  by  a  steel  plate  at  the  bottom, 
which  provides  an  air  space  under  the  tanks. 

I 
Stewart    and ;  Autocar.— The    Stewart   tank    (Fig.    230)    is 

mounted  in  a  wood  seat  frame.  However,  steel  straps  are  at- 
tached to  the  tank  and  form  brackets  which  rest  on  wood  sills. 


0 


1        1 

TANK 
<-  STEEL   STRAPS-^ 

= 

FIG.  230.     Stewart  Gasolene  Tank  and  Mounting. 

The  Autocar  tank  (Fig.  231)  is  formed  from  a  sheet  but  the 
ends  do  not  lap,  as,  a  pressed  cover  is  used.  The  heads  are  also 
pressed  and  set  into  the  body.  This  construction  permits  riveting 
and  soldering  the  head  and  all  parts,  while  the  cover  which  re- 
ceives very  little  strain  is  soldered.  This  tank  is  mounted  on 
steel  brackets  riveted  to  the  frame  and  is  retained  by  two  rods 
which  are  supported  by  two  brackets  riveted  and  soldered  to  the 
tank. 

Several  makers  use  tanks  which  are  drawn  from  one  sheet  of 
metal  and  have  but  one  soldered  joint.  This  type  of  tank  is  illus- 
trated in  Fig.  232,  which  illustrates  the  mounting  of  the  United 
States  trucks.  These  tanks  are  tinned  inside  and  out  and  the 
bead, is  soldered  „  as  shown. 


THE  FUEL  SUPPLY  SYSTEM 


249 


The  United  States  mounting  consists  of  a  separate  frame  or 
cradle,  very  rigid,  having  two  brackets  which  rest  on  the  vehicle 
frame,  connected  by  a  steel  channel  and  a  tie  rod.  Raybestos  is 
riveted  to  the  brackets  to  give  a  cushion  effect,  and  the  tank  is 
retained  by  two  steel  straps.  Gasoline  feed  is  by  gravity  through 


FILLER- 


-r 

RETAINING  ffOD  [^ 
AND  BRACKETS  I 

1 

1 

°                                                                                                                                                                 0 

C 

0                                                                                                                RIVET  •" 

Q                                                                                                                                                                                                                                 0 

IT  » 

OUTLET  — 

FIG.  231.     Autocar  Tank  with  Riveted  and  Soldered  Ends. 

a  strainer  attached  to  the  tank  and  supported  from  the  tank 
mounting. 

Gasoline  tanks  when  soldered  and  placed  under  the  seat,  have 
given  some  trouble  due  to  leaks,  as  in  some  cases  it  is  quite  dif- 
ficult to  hold  the  tank  in  such  a  way  as  to  prevent  vibration  from 


FIG.  232.     U.   S.   Pressed   Steel   Tank  and  Mounting. 

cracking  the  solder  at  the  joints.  The  gasoline  supply  pipe  also 
has  its  disadvantages  since  when  the  motor  is  placed  under  a 
hood,  this  pipe  becomes  quite  long  and  it  is  difficult  to  keep  it 
free  from  leaks. 

In  order  to  overcome  these  objections  these  tanks  on  the  Denby 
and  Union  trucks  are  mounted  on  the  dash,  the  Union  mounting 


250    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


is  illustrated  in  Fig.  233.  This  position  provides  the  shortest  gaso- 
line line,  reducing  the  dan- 
ger of  leaks  due  to  vibration, 
while  it  also  provides  an 
ample  head  of  fuel  for  grav- 
ity feed.  This  tank  is  sup- 
ported by  brackets  and 
straps  and  is  provided  with 
a  strainer  and  shut-off  valve. 
In  the  pressure  feed  sys- 
tem either  the  pressure  of 
the  exhaust  gases  or  air 
pressure  from  a  mechanical 
driven  pump  is  used  to 
force  the  gasoline  to  the  car- 
buretor float  chamber.  This 
system  requires  consider- 
able piping,  a  pressure  gage, 
a  pressure  regulator  or 


TIG.  233.     Union    Tank   Mounting. 

Stewart  Vacuum  Feed. 

—The  Stewart  vacuum 
feed  is  used  on  the  Knox 
tractor,  Kissel  Kar  trucks 
and  others  and  is  shown 
in  Fig.  234.  The  mechan- 
ism is  contained  in  a  cy- 
lindrical tank  which  may 
either  be  mounted  on  the 
engine  or  on  the  dash- 
board. The  tank  is  di- 
vided into  two  chambers, 
the  upper  one  being  the 
filling  chamber  and  lower 
the  emptying  chamber. 
The  former  contains  a 
float  valve  and  the  con- 
nections to  the  intake 
manifold  and  the  main 
fuel  tank.  The  lowTer 
chamber  has  a  connection 
leading  to  the  carburetor. 


pump  and  a  hand  pump. 


CONM£CTtON  TO 
GA&QL£N£   TANK 


CONNECTION  TO 
CARBURETOR 


FIG.  234.     Stewart  Vacuum  Tank. 


This  lower  chamber  is  always  under 


atmospheric  pressures  as  the  flow  of  gasoline  from  it  is  by  gravity 


THE  FUEL  SUPPLY  SYSTEM 


251 


SAFETY  VALVE 
ADJUSTING  SCftfW 


SAFETY  VALVt 


SIEVE 


—PIPE  TO 
GASOLINE  TANK 


only.  Atmospheric  pressure  is  maintained  by  an  air  vent  which 
communicates  with  the  chamber.  The  suction  of  the  piston  on 
the  intake  stroke  creates  a  vacuum  in  the  upper  chamber,  which 
closes  a  valve  between  the  two  chambers  and  in  turn  draws  gaso- 
line from  the  main  tank.  The  gasoline,  as  it  is  being  sucked  into 
the  upper  chamber  operates  a  float  valve.  When  this  float  valve 
has  risen  to  a  certain  mark,  it  automatically  shuts  off  the  suction 
valve  and  opens  an  air  valve.  This  open  air  valve  creates  an 
atmospheric  condition  in  the  upper  chamber  and  gasoline  imme- 
diately commences  to  flow  to  the  emptying  chamber.  When  the 
float  is  at  the  bottom  of  its 
chamber,  the  suction  valve 
is  open  and  the  air  valve 
is  closed.  The  lower 
chamber  has  a  flap  valve 
which  prevents  the  gaso- 
line in  the  lower  chamber 
from  being  sucked  into 
the  upper  chamber,  as  the 
float  falls  and  opens  the 
suction  valve. 

On  the  Knox  Tractor  the 
gasoline  tank  is  mounted 
on  the  running  board  and 
the  engine  suction  through 
the  system  described 
above  draws  gasoline  from 
the  main  tank  and  sup- 
plies the  carburetor. 

Saurer  Gasoline  Feed  System.— The  Saurer  truck  uses  a  pres- 
sure feed,  the  gasoline  tank  being  located  under  the  driver's  seat 
and  above  the  level  of  the  carburetor  when  the  tank  is  full.  On 
the  special  Saurer  carburetor,  however,  it  was  found  that  a  con- 
stant pressure  was  essential  to  its  proper  functioning  and  the 
gasoline  tank  was  moved  from  the  rear  of  the  truck  to  the  driver's 
seat.  Fig.  235  is  a  cross-section  of  the  exhaust  pressure  device. 

The  exhaust  gas  enters  and  passes  through  a  screen  to  remove 
carbon  and  fire,  any  small  particles  falling  to  the  bottom  of  the 
long  tube  which  can  be  removed  for  cleaning.  The  gas  then 
passes  to  the  other  chamber  through  the  valve  which  it  lifts. 
The  valve  is  returned  to  its  seat  by  a  spring  to  retain  the  pres- 
sure in  this  chamber  and  prevent  its  escape  back  into  the  exhaust 


AND  SED/HENT 
COLLECT  HEft£ 


FIG.  235.     Saurer  Pressure  Device. 


252    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

manifold  in  the  interval  between  exhausts.  The  upper  valve  is  a 
sort  of  safety  valve  to  prevent  the  pressure  from  becoming  too 
great.  This  valve  is  regulated  by  the  knurled  screw  on  top  of 
the  device.  The  pressure  is  maintained  at  about  two  pounds. 

Advantages  and  Disadvantages. — Each  system  has  its  advan- 
tages and  its  disadvantages.  Gravity  is  an  absolutely  depend- 
able and  constant  force  which  acts  independently  of  an  artificially 
created  condition,  and  can  be  implicitly  relied  upon  to  cause  the 
flow  of  fuel  to  the  carburetor  so  long  as  the  pipe  is  unobstructed 
and  the  upper  surface  of  the  fuel  supply  is  at  a  higher  level  than 
the  gasoline  level  in  the  carburetor  float  chamber.  It  is  the  most 
simple  system  on  account  of  the  simplicity  of  piping  and  fittings 
and  there  is  practically  nothing  to  keep  in  order. 

The  chief  disadvantage  is  that  the  pressure  under  which  the 
fuel  is  supplied  to  the  carburetor  is  variable.  Not  only  does  it 
diminish  progressively  as  the  fuel  level  in  the  tank  falls,  on  ac- 
count of  the  reduction  of  the  gravity  head  acting,  but  it  also 
diminishes  whenever  that  portion  of  the  vehicle  which  carries  the 
tank  stands  at  a  lower  level  than  that  which  supports  the  car- 
buretor. 

With  a  forced  system,  as  long  as  the  artificial  pressure  is 
maintained,  there  is  almost  a  certainty  that  gasoline  will  con- 
stantly be  fed  to  the  carburetor  entirely  independent  of  every 
other  conditions. 

The  system  possesses  disadvantages  in  that  there  are  numerous 
pipes  and  joints  which  must  be  kept  tight  in  order  that  the  tank 
may  hold  its  pressure  and  the  multiplicity  of  pipes  and  fittings 
adds  to  the  possibility  of  leaks  due  to  vibration. 

The  vacuum  system  is  by  far  more  simple  than  the  forced 
system  and  eliminates  the  pressure  pump,  gages,  regulator,  a  num- 
ber of  fittings  and  an  air-tight  tank.  Leaks  in  pipes  are  ma- 
terially reduced  as  the  pressure  is  very  low.  Like  the  forced 
system  it  will  supply  gasoline  to  the  carburetor  regardless  of 
grade,  vehicle  position  or  head  of  gasoline  in  the  main  tank. 

This  vacuum  tank  must  not  be  installed  in  the  exhaust  side  of 
the  engine,  as  gasoline  may  leak  or  overflow  from  the  tank  and 
cause  explosions  or  fires.  Proper  operation  of  the  system  depends 
entirely  upon  the  float  valve  and  if  it  develops  a  leak  it  cannot 
shut  of!  the  suction  valve  as  it  becomes  too  heavy  to  rise.  Par- 
ticles of  dirt  may  also  cause  trouble  by  holding  the  flap  valve 
open,  which  will  render  the  system  inoperative.  The  piping  is 
also  subject  to  the  danger  of  vibration. 


CHAPTER  XIX 

CONTEOLS 

THE  controls  of  a  commercial  car  consist  of  the  following: 
the  spark,  throttle,  clutch,  change  gear  lever,  brakes  and  the  steer- 
ing gear. 

The  most  important  controls  are  the  spark  and  throttle.  The 
former  may  either  be  hand  operated  from  the  steering  wheel,  it 
may  be  so  arranged  as  to  cause  ignition  to  occur  at  a  predeter- 
mined point  or  it  may  be  automatically  controlled  by  the  engine 
speed.  The  throttle  may  either  be  controlled  by  the  driver  or 
automatically.  There  are  two  means  of  manual  control,  by  hand 
or  foot.  Automatic  control  was  described  in  the  chapter  on 
governors. 

The  conventional  type  of  control  for  cars  with  sliding  gear 
transmissions,  comprises  two  pedals  located  on  opposite  sides  of 
the  steering  posts,  the  one  at  the  left  being  the  clutch  pedal  and 
the  one  at  the  right  the  brake  pedal.  The  foot  throttle  or  ac- 
celerator, if  one  is  provided,  is  placed  either  between  or  to  the 
right  of  these  pedals  for  operation  with  the  right  foot.  The 
mounting  of  these  pedals  depends  upon  the  general  construction 
of  the  vehicle.  When  a  unit  power  plant  is  used  they  are  gen- 
erally mounted  on  the  clutch  housing;  if  the  transmission  is 
mounted  amidships  the  common  plan  is  to  provide  a  tubular 
shaft  extending  partly  or  entirely  across  the  frame,  which  is  car- 
ried in  brackets  secured  to  the  frame.  Formerly  the  steering 
column  was  nearly  always  placed  on  the  right  side  of  the  car, 
and  the  hand  levers  for  operating  the  sliding  gears  and  the  emer- 
gency brake  were  located  just  outside  of  the  driver's  seat  on  the 
right.  However,  during  the  past  years,  quite  a  few  makers  have 
resorted  to  the  left-side  drive  in  which  the  steering  column  is 
located  on  the  left  side  and  the  levers  either  on  the  left  side  or  in 
the  center. 

On  several  makes  of  vehicles  the  clutch  and  service  brake  are 
operated  by  a  single  pedal.  The  first  motion  of  the  pedal  re- 
leases the  clutch  and  a  continued  motion  applies  to  service  brake. 
The  emergency  brake  may  also  be  operated  by  a  pedal ;  however, 
it  must  be  provided  with  a  ratchet  lock.  The  brakes  and  clutch 

253 


254    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

may  also  be  connected  through  suitable  linkage  so  that  when 
either  brake  is  applied  the  clutch  will  also  be  disengaged.  The 
idea  which  led  to  this  construction  undoubtedly  was  that  if  the 
driver  wants  to  stop  quickly  he  should  simultaneously  disengage 
the  clutch  and  apply  the  brake,  so  that  the  driving  effort  ceases 
and  no  braking  effort  need  be  expended  in  dissipating  the  energy 
stored  in  the  flywheel. 

In  order  to  prevent  shifting  of  the  gears  while  the  clutch  is 
engaged,  some  designers  have  provided  an  interlock  between  the 
gear  sliding  and  clutch  mechanism.  This  is  generally  so  ar- 
ranged that  the  gears  cannot  be  shifted  unless  the  clutch  is  out, 
and  the  clutch  cannot  engage  unless  the  gears  are  in  full  mesh. 

The  advantages  and  disadvantages  of  the  two  control  posi- 
tions may  be  divided  into  general  and  mechanical.  The  advan- 
tages of  one  are,  moreover,  usually  the  disadvantages  and  advan- 
tages of  the  other,  so  the  question  may  be  discussed  for  one  only. 
The  two  essential  features  of  the  left  side  control  are:  first, 
greater  ease  in  getting  out  of  the  vehicle  on  the  right  side,  and 
second,  the  bringing  of  drivers  meeting  vehicles  next  to  each 
other,  lessening  the  dangers  of  collision. 

The  first  is  of  importance  only  as  regards  convenience  of  both 
operator  and  helper.  The  second  point  is  well  worthy  of  con- 
sideration, as  when  two  vehicles  meet  on  narrow  streets  or  roads, 
the  distance  between  the  two  must  be  judged  with  great  nicety 
in  order  to  prevent  scraping  mud  guards  or  bodies  and  locking 
wheels.  The  disadvantages  are  the  difficutly  of  judging  the  dis- 
tance from  the  curb,  the  distance  of  an  overtaken  vehicle  and  in 
some  cases  the  difficulty  in  mounting  the  control  levers. 

The  first  claim  seems  to  be  a  difference  of  opinion,  as  there  are 
some  who  claim  one  is  no  more  difficult  than  the  other.  However, 
if  the  distance  is  not  judged  properly  the  tires  will  suffer,  not 
mentioning  the  strain  imposed  on  the  wheels,  axles  and  steering 
knuckles  in  striking  curbs. 

In  overtaking  vehicles  the  driver  is  on  the  left  side,  and 
farthest  from  the  overtaken  vehicle,  and  this  would  seem  to  be 
offset  by  the  advantage  of  bringing  the  operators  of  meeting 
vehicles  next  to  each  other,  but  a  close  study  seems  to  point  in 
favor  of  the  right  side  control,  for  in  the  case  of  meeting  vehicles 
two  operators  are  watching  and  able  to  judge  distance,  while  in 
overtaking  vehicles  there  is  only  one  who  can  judge  the  distance. 

The  mechanical  points  relate  to  details  of  design  and  apply 
to  each  type;  however,  the  center  control  offers  an  advantage  in 


CONTROLS  255 

that  the  gear  lever  can  be  mounted  directly  on  the  transmission, 
thus  doing  away  with  superfluous  connections. 

Spark  and  Throttle  Controls. — Various  types  of  these  controls 
were  illustraed  in  Chapter  XIV,  describing  the  steering  gear. 
The  general  practice  is  to  incorporate  these  in  the  steering  gear, 
while  the  foot  throttle  or  accelerator  consists  of  a  small  pedal 
mounted  on  the  dash  or  foot  board  and  connected  with  the  hand 
throttle  in  such  manner 
that  it  can  be  operated 
without  changing  the  posi- 
tion of  the  throttle  lever  on 
the  wheel.  This  is  accom- 
plished by  a  slip  joint,  as 
shown  in  Fig.  236.  The 
accelerator  is  hinged  to  the 
steering  column  and  con-  FIG.  236.  Pierce  Throttle  Control, 
nected  to  the  carburetor 

throttle  lever  by  a  rod  which  carries  a  slip  joint.  This  joint  has 
an  extension  to  which  the  hand  throttle  is  connected.  The  ac- 
celerator is  normally  held  in  the  off  position  by  a  coiled  spring. 

Another  type  of  accelerator  was  illustrated  in  Fig.  176,  Chap- 
ter XIV,  showing  the  Reo  steering  gear. 

The  advantage  of  the  foot  throttle  is  that  it  permits  the 
operator  to  control  the  speed  of  the  engine  with  his  right  foot, 
thus  leaving  his  right  hand  free  to  change  gears,  and  the  left  to 
steer  the  vehicle.  The  advantage  of  quick  gear-shifting  is  not 
to  be  denied,  as  anything  which  tends  to  reduce  engine  racing, 
gear  clashing,  etc.,  is  quite  desirable.  However,  motor  trucks 
operate  on  solid  tires  and  the  floor  boards  are  constantly  vibra- 
ting, and  all  of  the  minor  shocks  which  the  vehicle  springs  do 
not  absorb  are  transmitted  to  the  cab.  This  vibration  makes  it 
quite  difficult  for  the  operator  to  keep  his  foot  steady,  as  the 
slightest  movement  of  his  foot  acts  directly  upon  the  throttle. 
Sudden  acceleration  is  another  disadvantage  which  is  to  be 
avoided.  The  hand  throttle  of  course  eliminates  this,  and  it  is 
possible  to  hold  it  stationary  on  the  quadrant.  Disadvantages  of 
the  hand  throttle,  besides  the  inconvenience  in  changing  gears, 
includes  the  danger  of  shifting  gears  without  throttling  down  the 
engine. 

Brake,  Clutch  and  Gear-shift  Controls. — There  are  two  gen- 
eral types  of  pedals,  the  straight  and  the  bent  type,  both  of  which 


256    MOTOK  TKUCK  DESIGN  AND  CONSTEUCTION 

are  illustrated.  These  pedals  have  to  pass  through  the  floor 
boards  and  their  shape  is  dependent  upon  the  room  available. 
They  may  either  be  drop  forgings  or  steel  castings,  and  vary  from 
10  to  16  inches  in  length,  depending  upon  the  required  leverage. 
Brake  and  change-gear  levers  are  generally  drop  forged  of 
I-beam  section,  and  in  most  cases  pivot  from  a  common  pivot 
axis.  The  change-gear  lever  of  selective  type  change  gears  moves 
in  an  H  segment  or  gate  and  does  not  require  a  latch  to  hold  it  in 
position.  However,  a  lock  is  sometimes  provided  to  obviate  the 
possibility  of  accidentally  engaging  the  reverse  gear.  A  latch 
lever  must  always  be  used  with  a  progressive  gear  control,  and 
the  emergency  brake  lever  must  also  be  provided  with  a  latch. 
There  are  two  general  types  of  selective  gear  controls  Avhich  are 
termed  the  sliding  shaft  and  swinging  lever  types.  While  all 
controls  may  be  classified  under  these  two  heads,  there  are  numer- 
ous variations  in  detail. 

Sliding  Shaft  Control  Set. — The  Pierce  five-ton  control  set 
(Fig.  237)  is  of  this  type  and  mounted  on  the  right  side  rail  of 


CHANGE  G£AR 


f/tAHf 

/  G£AFi  SL/O/HG    SHAFT 

BAUL  LOCH 

FIG.  237.     Pierce  Selective  Type  Control. 

the  frame,  as  the  controls  are  arranged  for  right  side  drive. 
This  selective  gear  control  comprises  a  sliding  shaft  to  one  end  of 
which  the  control  lever  is  rigidly  secured,  and  which  at  its  inner 


CONTROLS 


257 


end  carries  a  downwardly  extending  arm  which  is  arranged  to 
engage  with  a  semi-circular  slot  in  one  or  the  other  of  the  sliding 
shafts  of  the  transmission  which  carry  shifting  forks.  The  slid- 
ing shafts  are  provided  with  ball  locks,  which  help  to  find  the 
correct  mesh,  and  also  prevent  shifting  of  both  shafts  together. 
The  H  plate  or  quadrant,  which  guides  the  lever  in  shifting  to 
the  various  speeds,  is  placed  slightly  forward  of  the  emergency 
brake  lever  and  has  a  lock  controlled  by  thumb  latch  on  the  lever 


FIG.  238.     Brown-Lipe  Center  Control  Unit  for  Unit  Power  Plant 
Transmissions. 


handle  for  locking  out  the  reverse  gears.  The  gear  shifting 
mechanism  also  has  a  lock  which  prevents  shifting  gears  until 
the  clutch  has  been  disengaged.  This  consists  of  a  semi-circular 
cam  or  segment  keyed  to  the  sliding  shaft  of  the  control  set  and 
a  plunger  connected  with  the  clutch  pedal,  which,  while  the  clutch 
is  engaged  rests  in  holes  in  the  cam  surface.  To  shift  gears  the 
clutch  must  first  be  disengaged  which  also  disengages  the  plunger. 
18 


258    MOTOE  TKUCK  DESIGN  AND  CONSTRUCTION 

The  emergency  lever  is  of  the  spoon  latch  type  which  releases 
a  lock  fitting  into  the  ratchet  teeth  of  the  brake  quadrant. 

Another  type  of  sliding  shaft  control  is  shown  in  Fig.  238. 
This  is  furnished  by  the  Brown  Lipe  Co.  with  their  transmissions 
for  left  side  control,  and  is  used  on  a  number  of  commercial  cars. 
This  differs  from  the  one  above  in  that  the  control  lever  is  hinged 
to  the  sliding  shaft,  and  pivots  in  a  rectangular  shaped  quadrant. 
Instead  of  the  lever  sliding  with  the  shaft,  it  pivots  to  either 
side  in  the  quadrant  and  moves  the  shaft  in  the  opposite  direction 
to  which  the  lever  is  moved.  The  emergency  brake  lever  has  a 
spoon  latch  which  operates  on  the  conventional  ratchet  quadrant, 
and  is  pivoted  from  the  same  center  as  the  gear  lever,  but  its 
shaft  extends  to  opposite  side  of  the  housing,  which  encloses  the 
entire  control.  This  type  of  control  is  intended  for  unit  power 
plants  where  the  transmission  usually  is  located  under  the  foot 
boards. 

The  Swinging-lever  Type. — A  swinging-lever  type  of  control 
used  on  several  cars  is  shown  in  Fig.  239,  and  is  designed  for 
right-side  control  and  frame  mounting.  The  change  gear  lever 


SHORT  LEVER 
PROWDED   W/TH  LUGS 


QUADRANT  AM 
BRACKET 


°/VOl 
6HORT  LEVERS 

FIG.  239.     Swinging  Lever  Type  of  Control. 

is  pivoted  to  a  hub  which  is  free  to  turn  on  the  control  shafts.  On 
each  side  of  this  lever  are  short  levers  which  are  fastened  to  con- 
centric control  shafts,  each  of  which  extend  to  the  inside  of  the 
frame  and  carry  operating  arms.  These  arms  are  connected  to 
the  sliding  shafts  of  the  transmission  by  rods  and  clevises.  The 
upwardly  extending  levers  are  provided  with  lugs,  between  which 
the  control  lever  engages  when  it  is  pressed  in  the  direction  of 


CONTKOLS 


259 


the  particular  short  lever.  Some  provision  must  be  made  for 
holding  the  change-gear  lever  in  a  natural  position,  and  this  is 
accomplished  by  the  two  flat  springs  fastened  to  the  short  levers. 
When  the  control  lever  is  moved  in  one  of  the  slots  of  the  quad- 
rant it  is  connected  with  one  of  the  short  levers  and  turns  the 
shaft  to  which  that  lever  is  secured. 


FIG.  240.     Warner  Swinging  Lever  Arranged  for  Center  Control  with  Right 

Hand  Drive. 

Fig.  240  illustrates  another  type  of  swinging  lever  control 
which  was  introduced  by  the  Warner  Gear  Co.  for  unit  power 
plant  mounting.  It  differs  from  the  above  in  the  method  of  en- 
gaging the  control  lever  with  the  short  levers  that  turn  the  con- 
centric shafts.  These  have  small  arms  hinged  to  them,  which  are 
held  in  contact  with  the  control  lever  by  spiral  springs.  The 
pivoted  arms  have  a  lug  which  engages  in  a  slot  in  the  quadrant 
and  locks  each  shaft  in  position.  This  type  of  control  eliminates 
the  danger  of  turning  both  shafts  at  the  same  time.  It  also  in- 
corporates a  reverse  lock  controlled  by  a  thumb  latch  on  the  con- 
trol lever. 

Center  control  may  also  be  employed  with  the  transmission 
located  amidships  or  on  the  jackshaft.  An  excellent  example  of 
this  is  shown  in  the  United  States  control,  Fig.  241,  in  which  the 
support  for  the  gasoline  tank  is  used  to  support  the  control. 


260    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


FIG.  241.     United  States  Center  Control  Mounting. 

Center  Control  and  Pedal  Mounting. — On  the  Flint  delivery 
cars  the  center  control  and  pedal  mounting  is  incorporated  in  a 
single  unit  supported  from  the  sub  frame  as  shown  in  Fig.  242. 
The  control  set  is  of  the  swinging  lever  type;  however,  instead 
of  using  a  quadrant  and  concentric  shafts,  the  short  arms  are  con- 
nected with  two  parallel  shafts  which  are  provided  with  plunger 
locks.  The  short  levers  instead  of  pivoting  from  the  center  of 
the  control  lever,  slide  with  the  shaft.  This  construction  permits 
placing  the  sliding  shafts  in  the  transmission  directly  above  the 
gears,  making  a  direct  connection  and  eliminates  the  trouble 
usually  experienced  with  bent  connections. 


PARALLEL 
SHAFTS 


CHANCE 

GEAR 

LEVER 


FIG.  242.     Center  Control  and  Pedal  Mounting  of  Flint  Delivery  Cars. 


CONTEOLS  261 

A  large  bracket  extends  from  one  subframe  member  to  the 
other  and  has  bearings  at  its  rear  end  to  support  the  control  and 
brake  lever,  while  bearings  are  provided  at  the  front  end  of  the 
pedals  and  their  shafts.  The  service  brake  connection  is  made 
from  a  small  lever  cast  integral  with  the  brake  pedal,  while  the 
clutch  is  connected  to  the  pedal  through  a  yoke  and  levers,  keyed 
to  the  shaft.  The  brake  pedal  is  interconnected  with  the  clutch 
pedal  so  that  in  applying  the  brake  the  clutch  will  also  be  dis- 
engaged. 

Fig.  80  depicts  a  unit  power  plant  transmission  with  the 
center  control  and  pedal  mountings  for  left-side  drive.  The 
SAvinging  control  lever  instead  of  being  pivoted  at  its  lower  end, 
has  the  pivot,  which  is  of  spherical  shape,  a  short  distance  from 
its  end  and  rests  on  a  bracket  incorporated  with  the  transmission 
cover.  The  end  of  the  lever  engages  with  the  shifter  forks  in  the 
transmission  which  have  lugs  that  straddle  the  lever.  This 
makes  a  very  simple  control  and  eliminates  a  number  of  parts. 
The  emergency  brake  lever  is  mounted  at  the  side  of  the  trans- 
mission and  is  also  pivoted  a  short  distance  from  the  end.  The 
lower  end  has  a  connection  for  the  brake  rod  and  a  slot  through 
which  the  quadrant  is  inserted.  The  pedals  are  mounted  on  an 
extension  of  the  clutch  disengaging  shaft.  Both  of  these  are  free 
on  the  shaft,  but  the  clutch  pedal  is  connected  to  a  sector  which 
permits  pedal  adjustment  to  take  up  the  wear  of  the  clutch. 

Progressive  Type  Control. — In  the  progressive  type  of  trans- 
mission it  is  necessary  to  progress  from  one  speed  to  another  and 
for  this  reason  it  is  necessary  to  provide  a  control  which  has  a 
lock  for  each  speed  and  the  neutral  position.  The  Mogul  heavy 
duty  trucks  are  equipped  with  a  progressive  type  transmission 
which  is  built  in  a  unit  with  the  jackshaft,  while  the  operator's 
seat  is  placed  over  the  engine.  This  makes  it  difficult  to  arrange 
a  neat  control;  however,  in  the  Mogul  trucks  the  control  levers 
and  pedals  are  supported  from  a  single  bracket.  Both  gear  and 
brake  levers  pivot  from  the  same  center  and  are  mounted  upon 
concentric  shafts.  Since  a  lock  is  required  for  both  levers,  these 
are  equipped  with  spoon  type  latches.  The  pedals  also  pivot 
from  a  center  common  to  both,  but  this  is  somewhat  below  the 
center  of  the  levers  as  shown  in  Fig.  243. 

The  position  of  the  control  levers  also  makes  it  difficult  to 
obtain  a  direct  connection  to  the  sliding  shaft  in  the  transmis- 
sion. In  this  case  it  is  quite  simple  as  an  extra  long  lever  is 


262    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

pivoted  from  the  seat  support  which  connects  with  the  control 
lever  near  its  pivot  end,  while  the  other  end  is  connected  to  the 
sliding  shaft. 


CLUTCH 
OPERATING 
iAFT 


CLUTCH  PEDAL 


BRAKE 
EQUALIZERS- 


TROD  AND  LEVER 


FIG.  243.     Mogul  Brake,  Clutch  and  Progressive  Type  Gear  Control. 

Brake  Linkage. — Unless  the  breaking  force  applied  to  the  rear 
wheels  is  equalized,  that  is,  that  brakes  on  opposite  sides  produce 
equal  retarding  forces,  the  car  has  a  tendency  to  skid  and  brake 
adjustment  is  also  quite  difficult.  This  necessitates  an  equalizing 
device  in  the  brake  operating  linkage,  which  will  apply  an  equal 
retarding  effect  to  the  two  brakes  of  each  set.  This  equalizer  is 
dependent  upon  the  general  scheme  of  the  linkage  and  in  most 
cases  is  of  the  whiffletree  or  modified  whiffletree  type.  The  brake 
linkage  is  dependent  upon  the  general  layout  of  the  chassis. 

With  the  seat  mounted  over  the  engine,  it  is  necessary  to  ar- 
range this  so  it  will  provide  maximum  accessibility  for  the  en- 
gine, and  Fig.  243  illustrates  how  this  is  accomplished  with  wire 
cables  on  the  Mogul  trucks.  Short  rods  are  connected  with  the 
brake  pedal  and  lever  and  carry  turnbuckles  which  are  attached 
to  wire  cables.  These  cables  pass  over  pulleys  mounted  on  the 
seat  frame  and  the  clutch  disengaging  shaft.  They  connect  with 
a  cross  shaft,  which  in  turn  is  connected  with  equalizers  of  the 
whiffletree  type.  From  these  equalizers,  rods  and  clevises  form 
the  connections  to  the  brake.  The  clutch  connection  is  made  with 
a  rod  direct  from  the  pedal  to  the  clutch  disengaging  shaft  which 
is  supported  from  the  subframe. 


CONTROLS 


263 


On  the  Natco  trucks  (Fig.  244)  the  engine  is  mounted  under 
a  hood  and  the  linkage  consists  of  rods  throughout. 


CLUTCH  ANO  SEffV/CS 
PEOAL. 


CLUTCH   ft 00 


FIG.  244.     Natco  Brake  Eod  and  Pedal  Arrangement. 

The  pedals  are  supported  by  a  bracket  attached  to  the  frame, 
while  a  cross  shaft  is  arranged  to  incorporate  an  equalizer  for 
each  set  of  brakes.  The  clutch  pedal  also  operates  the  service 
brake,  while  the  brake  pedal  has  a  ratchet  which  locks  auto- 


FIG.  245.     Peculiar  Brake-Rod  Equalizer  of  the  U.  S.  Truck. 

matically  and  is  released  by  tipping  the  pedal  pad.  The  brake 
equalizer  is  of  a  modified  whiffletree  type  and  is  mounted  vertical 
instead  of  horizontal. 

An  equalizer  which  is  a  modification  of  the  bevel  gear  differ- 
ential, is  used  on  the  United  States  trucks  and  shown  in  Fig. 


264    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

245,  in  which  the  ordinary  brake  levers  which  usually  form  con- 
nections for  the  modified  form  of  whiffletree  equalizer  are  re- 
placed by  bevel  gear  sectors.  The  lever  to  which  the  brake  rod  is 
connected  has  a  spindle  upon  which  a  bevel  pinion  is  mounted 
which  meshes  with  the  bevel  sectors  on  opposite  sides.  This 
pinion  is  free  to  rotate  upon  its  spindle  and  as  the  brakes  are  ap- 
plied it  equalizes  the  pull  on  the  brake  rods  on  opposite  sides  of 
the  frame  in  the  same  way  as  the  differential  equalizes  the  power 
applied  to  the  rear  wheels. 


FIG.  246.     Wick  Oiling  System  on  the  La  France  2-Ton  Truck  Brake  Shafts. 

Most  brake  shafts  and  their  bearings  are  lubricated  grease 
cups ;  however,  on  the  La  France  trucks  the  brake  shaft  assembly 
(Fig.  246)  is  lubricated  by  oil.  Both  shafts  are  hollow  and  the 
inner  one  forms  the  oil  reservoir,  which  will  carry  sufficient  oil 
to  lubrciate  the  brake  levers  for  a  long  time.  Wicks  are  led  from 
the  central  oil  reservoir  to  the  various  bearings.  The  oil  is  put 
into  the  reservoir  conveniently  from  the  outside  of  the  chassis  at 
the  end  of  the  transverse  shaft. 


CHAPTER  XX 

THE  MUFFLER 

ALTHOUGH  it  is  not  essential  that  motor  trucks  operate  as 
quietly  as  pleasure  cars,  it  is  quite  essential  that  they  operate 
without  disagreeable  noise.  For  this  reason  the  exhaust  must  be 
muffled,  which  is  accomplished  by  passing  the  spent  gases  through 
a  muffler  before  they  are  discharged  into  the  atmosphere.  This 
muffler  is  sometimes  referred  to  as  a  silencer.  The  object  of  the 
muffler  is  to  permit  the  gases  to  expand  and  to  cool,  thereby  re- 
ducing the  pressure,  which  is  the  cause  of  the  noise  when  they  are 
discharged  into  the  atmosphere  directly.  It  is  quite  simple  to 
obstruct  the  passages  of  the  gases  from  the  engine  to  atmosphere, 
however,  in  order  to  discharge  them  without  disagreeable  noise, 
they  must  be  permitted  to  escape  very  freely,  so  that  they  will 
not  create  any  back  pressure  on  the  pistons  during  the  exhaust 
stroke. 

Muffler  not  Close  to  Engine. — In  most  cases  the  muffler  is 
mounted  as  far  away  from  the  engine  as  the  general  chassis  de- 
sign permits.  It  is  usually  mounted  under  the  frame  of  the 
vehicle.  This  arrangement  permits  the  engine  to  exhaust  into  an 
exhaust  pipe  of  considerable  length,  the  capacity  of  which  is 
sometimes  as  much  as  four  times  the  piston  displacement  of  one 
cylinder.  This  long  pipe  gives  the  gases  a  chance  to  cool  before 
they  reach  the  muffler,  while  the  latter  should  be  arranged  in  such 
a  manner  that  heat  may  rapidly  be  abstracted  from  the  gases. 

Mufflers  generally  consist  of  a  series  of  expansion  chambers 
which  communicate  by  means  of  fine  and  sometimes  tortuous  pas- 
sages, and  after  passing  through  these  chambers  the  gases  are 
finally  permitted  to  escape.  Mufflers  should  possess  certain  fea- 
tures, a  construction  which  permits  cleaning,  strength  to  with- 
stand pressures  of  gasoline — air  vapor  explosions  at  atmospheric 
pressure  and  ability  to  resist  vibration.  Cleaning  is  necessary,  as 
lubricating  oil  and  solid  carbon  particles  held  in  suspension  by 
the  gases  will  clog  the  fine  passages  and  increase  the  back  pres- 
sure. Some  mufflers  are  so  constructed  that  they  can  be  dis- 
mantled for  cleaning.  Explosions  in  the  muffler  are  frequent,  and 
it  is  essential  to  have  enough  strength  to  resist  this  pressure  with- 

265 


266    MOTOE  TRUCK  DESIGN  AND  CONSTRUCTION 

out  bursting.  The  walls  of  the  muffler  may  be  so  designed  as  to 
prevent  ringing  which  is  really  a  harmonious  vibration  of  suc- 
ceeding exhausts.  This  is  sometimes  accomplished  by  lining  the 
outer  shell  with  sheet  asbestos,  but  this  may  not  seem  very  de- 
sirable, as  it  possesses  certain  heat  insulating  qualities. 

The  final  outlet  is  generally  through  a  pipe  of  considerably 
less  cross  section  than  the  exhaust  pipe.  This  is  sometimes  flat- 
tened so  that  the  gases  escape  in  a  continuous  sheet.  In  some 
cases  this  is  accomplished  by  a  series  of  small  holes  in  the  final 
outlet  or  the  outer  shell. 

Cut-outs. — In  order  to  relieve  the  so-called  back  pressure  of 
the  muffler,  cut-outs  are  sometimes  provided,  which  are  placed 
forward  of  the  muffler  or  in  the  exhaust  pipe,  and  permit  ex- 
hausting the  gases  directly  into  the  atmosphere,  instead  of  hav- 
ing them  pass  through  the  muffler.  The  general  claim  for  this 
cut-out  is  that  it  adds  to  the  efficiency  and  power  of  the  engine. 
However,  it  has  been  proven  that  with  a  well  designed  muffler  a 
cut-out  is  of  little  value,  except  that  the  operator  may  occasion- 
ally listen  to  the  action  of  the  engine. 

Pierce  Muffler. — The  Pierce  muffler  (Fig.  247)  consists  of  two 
adjacent  cylindrical  chambers,  which  communicate  through  a 
number  of  holes  in  the  inner  chamber.  The  outer  chamber  is 
divided  into  three  expansion  chambers,  while  the  inner  member 


BRACKI  r 

CENTRAL  TUBE 
—eVHNSK,*  CHAMBER  /  t*-°  EXPANSION  CHAMBER       /v  expAN3,w 


-—-  *-— ^f?,- 


,  I      -      \j™«°0  _  ji  !       _&_JLJL 


FIG.  247.     The  Pierce  Muffler. 

is  also  divided  into  three  parts,  the  partitions  of  each  member 
being  pressed  steel  discs.  The  gases  first  enter  the  inner  chamber 
and  pass  through  perforations  into  the  outer  chamber  and  from 
this  chamber  they  return  to  the  second  portion  of  the  inner  cham- 
ber and  thence  into  the  second  expansion  chamber,  thence 
through  the  central  member  into  the  third  expansion  chamber 
and  back  into  the  central  member  from  which  they  are  dis- 
charged. This  muffler  is  mounted  parallel  to  the  side  members  of 
the  frame  and  has  cast  end  plates  which  have  integral  brackets 
for  frame  mounting.  The  tubular  members  and  end  plates  are 


THE  MUFFLEE 


267 


held  together  by  long  tie  rods  which  extend  the  full  length  of 
the  muffler. 

Packard  Muffler. — The  Packard  muffler  (Fig.  248)  also  con- 
sists of  an  inner  and  outer  chamber  with  cast  end  plates,  retained 


FIG.  248.     The  Packard  Muffler. 

by  tie  rods.  However,  the  necessary  volume  is  obtained  by  in- 
creasing the  diameter  instead  of  making  the  muffler  of  consid- 
erable length.  The  inner  chamber  has  a  series  of  small  holes, 
through  which  the  gases  pass  after  expanding  in  the  inner  cham- 
ber. After  expanding  in  the  outer  chamber  they  escape  at  the 
rear  end.  This  outer  chamber  is  insulated  with  sheet  asbestos 
retained  by  plates  and 
small  screws  to  deaden  the 
vibration.  The  support- 
ing brackets  are  made  of 
pressed  steel  and  fit  into 
the  side  members  of  the 


TCft    EXPANSION    CHAMBfft 


frame. 


FIG.  249.     The  Gray-Hawley  Muffler. 


Gray-Hawley  Muffler.— The  Gray-Hawley  muffler  (Fig.  249) 
is  used  on  a  number  of  commercial  cars  and  consists  of  two  cast 
heads  which  support  three  cylindrical  sheet  metal  tubes.  The 
gases  enter  the  inner  one  of  the  three  members  from  the  exhaust 

pipe.  They  expand  in 
this  chamber  and  then 
pass  through  fine  per- 
forations at  the  opposite 


HS/O/V  CHAMBERS 


FIG.  250.     The  U.  S.  Muffler  with  Cutout.     end  in  the  Partition  wall 

into       the       intermediate 

chamber,  and  thence  through  similar  perforations  at  the  rear  end 
of  the  innermost  portion  wall  into  the  outer  chamber  from  which 
they  escape  at  the  further  end.  The  path  of  the  gases  is  shown 
by  the  arrow-heads  in  this  illustration. 

United  States  Muffler. — The  United  States  trucks  are  equipped 
with  the  muffler  shown  in  Fig.  250  which  is  similar  to  the  one 


268    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


previously  mentioned.  The  gases  take  the  same  path  and  are  ex- 
panded in  a  similar  manner.  However,  they  are  discharged 
through  perforations  at  the  center  of  the  outer  chamber,  as  this 
muffler  is  mounted  crosswise  at  the  rear  end  of  the  subframe. 
Into  the  head,  which  connects  with  the  exhaust  pipe,  a  cut-out  is 
placed.  This  cut-out  consists  of  a  poppet  valve,  held  to  its  seat 
by  a  spring  and  bell  crank  pivoting  in  a  bracket  operated  through 
suitable  linkage  from  the  operator's  seat.  When  this  cut-out  is 
opened  by  raising  the  valve  from  its  seat,  the  greater  part  of  the 
gases  take  the  path  of  the  least  resistance,  which  is  through  the 
valve  opening  instead  of  passing  through  the  various  expansion 
chambers. 

Riker  Muffler. — The  Riker  muffler  (Fig.  251)  is  somewhat 
similar  to  those  depicted  above,  except  that  the  inner  chamber  is 
perforated  at  both  ends  and  the  outlet  is  of  a  different  shape. 
Both  end  plates  or  heads  are  provided  with  flat  surfaces  to  which 

the  supporting  brackets 
are  bolted.  The  front  head 
has  an  opening  against 
which  a  flat  valve  is  held 
through  the  pressure  ex- 
erted by  a  coiled  spring  at- 
tached to  the  end  of  a  bell 

crank  and  the  head.  The  bell  crank  supports  the  valve,  which  is 
raised  from  its  seat  when  the  cut-out  pedal  is  depressed.  Both 
exhaust  and  outlet  pipes  are  attached  to  the  muffler  heads  by 
flanges  and  bolts. 

Powell  Muffler. — The  Powell  muffler  is  also  used  by  some 
makers  of  commercial  vehicles.  This  consists  of  a  number  of 
pressed  steel  cups,  the  open 
ends  of  which  are  flanged 
out  so  as  to  fit  over  the 
closed  end  of  the  adjacent 
section  or  cup.  Each  of 
the  cups  A  are  perforated 


FIG.  251.     Eiker  Muffler  and  Cutout. 


FIG.  252.     The  Powell  Muffler. 


and  through  these  perfor- 
ations the  adjacent  cham- 
bers communicate.  Cups 
B  and  G  are  used  at  the 

rear  end  and  are  so  arranged  as  to  form  a  somewhat  tortuous 
passage  for  the  gases.    This  is  accomplished  by  a  series  of  small 


THE  MUFFLER 


269 


perforations  in  cup  B  while  cup  C  has  a  large  central  hole.  Three 
tie  rods  hold  the  various  sections  together,  which  permits  using 
any  number  of  cups  to  meet  the  requirements  of  each  individual 
engine  to  which  the  muffler 
may  be  fitted.  Fig.  252 
shows  this  muffler  as  ap- 
plied to  the  Mogul  trucks, 
and  Fig.  253  illustrates  its 
application  to  the  Knox 
tractor,  in  which  it  is 
mounted  crosswise  at  the 
front  end  of  the  frame. 


FIG.  253.     The  Knox  Tractor  Muffler. 


Denby  Muffler. — A  pressed  steel  muffler  has  recently  been  in- 
troduced by  Gueder,  Paeschke  &  Frey  Co.,  which  is  used  on  the 
Denby  trucks.  This  is  illustrated  in  Fig.  254,  and  consists  of  a 
number  of  pressed  steel  cups  placed  in  a  steel  shell  and  elec- 
trically welded.  This  makes  a  very  light  construction  and  the 
claim  is  made  that  it  weighs  but  five  pounds.  The  gases  enter  at 


-MUFFLER  SHELL 


CONICAL  CUPS 


FIG.  254.     The  G.  P.  &  F.  Muffler. 

the  forward  end  and  pass  through  conical-shaped  cups  which 
are  so  spaced  that  an  expansion  chamber  is  formed  between 
them.  The  remaining  cups  are  of  similar  shape,  but  reversed  in 
position  and  also  provide  limited  expansion  chambers  between 
them.  The  first  of  these  is  perforated,  while  the  second  has  but 
one  large  central  hole,  and  the  third  has  but  half  the  number  of 
perforations  of  the  first  one.  The  outlet,  instead  of  having  one 
large  central  opening,  is  also  perforated,  so  that  the  gases  escape 
in  continuous  streams. 

Fig.  255  depicts  another  popular  type  of  muffler  known  as  the 
"  Dunco,"  which  operates  on  a  principle  of  automatic  adjustment 
which  is  that  of  the  well-known  steam  ejector.  A  portion  of  the 
exhaust  gases  pass  directly  through  a  central  tube  to  a  high  speed 
jet,  at  the  outlet  of  that  tube,  and  induce  a  partial  vacuum  be- 
hind them,  thus  drawing  the  remaining  gases  through  baffle 
plates  or  cones  in  the  muffler.  It  is  claimed  that  this  muffler  is 


270    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


self-adjusting  to  variations  in  speed,  and  the  frequency  of  in- 
jector impulses  varies  directly  as  the  speed  of  the  engine,  so  that 
the  pull  of  the  ejector  is  always  proportional  to  the  volume  of 


FIG.  255.     Bunco  Ejector  Type  Muffler. 

gas  to  be  drawn  through  and  discharged.  The  heads  are  mal- 
leable castings  and  tie  rods  hold  the  entire  construction  together, 
so  that  it  is  very  simple  to  take  the  muffler  apart  for  cleaning. 

Maxim  Silencer. — The  Maxim  silencer  (Fig.  256)  incorporates 
a  somewhat  different  principle  in  which  but  one  tubular  member 

is  used.  The  interior  con- 
struction is  of  a  peculiar 
built  spiral  chamber,  which, 
it  is  claimed,  can  not 
clog  or  collect  carbon.  The 
gases  enter  at  one  end  and 
pass  from  inlet  to  outlet 
without  obstructions  of 
any  kind.  This  contin- 
uous channel  has  the  pecul- 
iarity of  circular  or  helical  form,  and,  owing  to  the  centrifugal 
force  of  the  fast  moving  gases,  these  gases  whirl  to  the  outer 
periphery,  traveling  an  approximate  distance  of  three  and  one- 
half  times  the  length  of  the  muffler.  Slow  moving  gases  will  re- 
main at  the  center  and  grad- 
ually move  forward  to  the 
outlet.  The  heads  are  mal- 
leable, while  the  shell  is 
made  of  sheet  steel,  seamed 
and  electrically  welded  to  FIG.  257.  The  Old  Berg  Muffler. 
prevent  bursting. 

Oldberg  Muffler.— The  Oldberg  muffler  (Fig.  257)  has  a  series 
of  expansion  chambers.  The  gases  enter  the  center  member  and, 
due  to  the  arrangement  of  the  perforations,  immediately  start 


FIG.  256.     The  Maxim  Silencer. 


THE  MUFFLER 


271 


to  pass  out  and  around  to  the  opposite  side.  Each  alternate  tube 
is  placed  eccentrically  with  respect  to  the  axis  of  the  muffler. 
The  perforations  in  each  tubular  member  are  arranged  in  two 
rows  throughout  their  length.  The  total  area  of  these  perfora- 
tions is  greatly  in  excess  of  the  area  of  the  exhaust  pipe  con- 
necting with  the  muffler.  The  sound  waves  are  interrupted  by 
passing  half  of  the  gases  around  each  side  of  the  tubular  mem- 
bers, the  two  streams  coming  together  on  the  opposite  side  of  the 
preceding  chamber. 


FRAME  SIDE  MEMBER 


HEAD    WITH 
'/NTFfEOAL    BRACKET 


EXPANSION  CHAMBER 


/ 


CENTRAL  TUBE 


OUTLET 
eXHAUST   PIPE 


•PACK/NG 
'LAMP  NUT 


FIG.  258.     The  I.  H.  C.  Muffler  for  Two-Cylinder  Opposed  Motor. 

The  mufflers  described  above  apply  to  four  and  six  cylinder 
engines,  while  Fig.  258  illustrates  the  I.H.C.  construction  for 
their  two-cylinder  engines.  It  consists  of  an  inner  and  outer 
shell  with  cast  heads  retained  by  a  single  tie  rod.  The  gases 
enter  the  outer  chamber  near  its  center  through  exhaust  pipes 
from  each  cylinder.  They  expand  in  this  outer  chamber  and  pass 
through  perforations  in  the  walls  of  the  inner  member,  whence 
they  escape  at  both  ends,  as  the  muffler  is  mounted  crosswise  at 
the  rear  end  of  the  frame.  The  outlets  and  mounting  brackets 
are  cast  integral  with  the  muffler  heads.  The  end  view  illustrates 
the  method  of  retaining  the  exhaust  pipes  with  packing  joints. 

The  exhaust  system  begins  with  the  exhaust  manifold  of  the 
engine  and  includes  the  exhaust  pipe,  cut-out  and  muffler.  Prac- 
tice differs  with  the  various  makers  however.  What  has  been 
outlined  in  this  and  previous  chapters  on  the  engine  serves  to 
give  a  general  idea  of  the  subject. 


CHAPTER  XXI 

MOTOR  TRUCK  WHEELS 

ROAD  shocks  must  first  be  taken  by  the  road  wheels,  through 
tire  contact,  and  thence  distributed,  spreading  out  in  all  direc- 
tions from  the  hubs  of  the  wheels. 

There  are  essentially  three  types  of  wheels  used  on  motor 
trucks  at  present:  wood  wheels  of  the  artillery  type  which  are 
used  on  a  great  number  of  machines,  pressed  steel  and  cast  steel 
wheels. 

Artillery  Wood  Wheels.— The  artillery  type  of  wheel  consists 
of  a  set  of  spokes  turned  from  very  tough  wood,  generally  sec- 
ond growth  hickory,  which  are  clamped  at  their  inner  end  be- 
tween flanges  on  a  metal  hub  and  at  their  outer  end  tenoned  into 
a  wooden  felloe,  which  is  surrounded  by  a  steel  band  or  ring. 
The  spokes  may  be  either  of  elliptic,  square  or  rectangular  sec- 
tion, and  great  care  is  taken  to  get  the  fiber  to  run  exactly  in  the 
direction  of  the  spoke  length.  It  is  common  practice  to  split  the 
spoke  billets  instead  of  sawing  them. 

The  wood  used  in  the  spokes  and  felloes  is  made  from  well- 
seasoned  timber,  so  that  strength  and  toughness  in  the  highest 
degree  can  be  obtained.  Second  growth  stock  and  stock  from  the 
lower  portion  of  small  trees  yields  the  best  parts. 

In  truck  work  when  solid  tires  are  used  the  spokes  are  of 
square  or  rectangular  section,  since  these  are  stronger  in  propor- 
tion to  weight  than  the  elliptic  spoke. 

The  greatest  amount  of  trouble  with  the  artillery  wheel  has 
been  experienced  with  those  used  on  very  heavy  trucks.  The 
spokes  are  very  thick  and  a  comparatively  slight  shrinkage  of 
the  spoke  causes  them  to  loosen  in  their  hub  and  the  severe  jar- 
ring, due  to  the  use  of  solid  tires,  then  has  a  very  destructive 
action.  In  order  to  deviate  this  difficulty  and  strengthen  the 
spokes  assembly  at  the  center  the  Schwartz  Wheel  Co.  make  the 
miter  of  the  spokes  interlocking,  while  other  makers  provide  keys 
between  the  miters  or  adjacent  spokes. 

Steel  Wheels. — Cast-steel  wheels  are  now  gradually  coming 
into  use,  while  pressed  steel  wheels  are  also  used  on  some  of  the 

272 


MOTOR  TRUCK  WHEELS 


273 


vehicles  having  less  than  two  tons  capacity.  The  steel  wheel  is 
very  popular  in  foreign  countries,  and  American  manufacturers 
are  gradually  using  them.  In  some  cases  they  have  not  succeeded, 
while  in  others  they  have  given  excellent  service,  which  is  also 
true  of  the  wood  wheel. 

The  advantages  possessed  by  the  steel  wheel  for  heavy  duty 
are  strength,  true  shape,  rigidity,  concentricity  of  the  hub  and 
accurate  design  for  the  support  of  the  load.  In  point  of  strength 
and  elastic  limit,  the  steel  wheel  well  made,  is  superior  to  the 


FIG.  259.     Natco  Front  Wheel. 

wood  wheel,  and  will  sustain  more  in  impact  and  side  thrust. 
Another  advantage  is  that  they  may  be  accurately  machined  and 
once  round,  they  will  stay  so  regardless  of  humidity,  heat,  etc., 
that  affect  most  wood  wheels.  In  design  these  wheels  may  have 
the  brake  drum,  hub  and  flange  cast  integral  so  that  there  are  no 
bolts  and  rivets  to  loosen  or  break.  Considering  weight,  for 
vehicles  of  three-ton  capacity  and  over,  the  steel  wheel  is  lighter 
than  a  wood  wheel  of  equal  strength,  while  for  two-ton  vehicles 
both  types  are  about  equal  in  weight. 

The  pressed  steel  type  of  wheel  for  trucks  up  to  two-tons 
capacity  is  somewhat  lighter  in  weight  than  a  wooden  wheel  of 
corresponding  capacity.  This  tjpe  of  wheel  can  be  produced  for 
practically  the  same  price  as  wood  wheels,  when  the  complete 
wheel  is  considered. 

The  steel  wheels  vary  in  construction,  and  opinions  differ  as 
to  which  construction  gives  the  best  service. 
19 


274    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

An  idea  of  the  construction  of  wood  and  steel  wheels  can  be 
obtained  from  the  illustrations  presented  herewith  and  the  de- 
scriptions which  follow : 

Fig.  259  illustrates  the  Natco  one-ton  front  wheel  with  de- 
mountable tire.  The  wheel  has  twelve  square  spokes  which  are 
turned  into  the  felloe  and  retained  in  the  hub  by  twelve  bolts 
placed  between  adjacent  spokes.  The  general  form  of  the  hubs 
is  largely  determined  by  the  dimensions  of  the  bearings  and  their 
necessary  distance  apart.  One  hub  flange  is  generally  made  in- 
tegral with  the  hub  casting,  while  the  other  is  free  to  be  slipped 
over  a  machined  cylindrical  surface  so  as  to  be  accurately  guided. 


FIG.  260.     Mogul  Wheel   Spoke,  Felloe  and  Felloe  Band  Assembly. 

Fig.  260  depicts  the  construction  of  the  Mogul  six-ton  rear 
wheel  which  is  equipped  with  40  X  7  in.  S.A.E.  tires.  There  are 
eight  spokes  of  rectangular  section  and  eight  spokes  of  square 
section.  These  are  all  of  the  same  thickness,  but  the  rectangular 
ones  are  used  for  attaching  the  brake  drum,  and  practically  the 
same  strength  as  the  square  spokes,  as  considerable  stock  is  re- 
moved by  the  bolt  holes.  The  hub  bolts  pass  through  the  miter 
joints  of  adjacent  spokes  as  shown.  The  felloe  is  made  to  S.A.E. 
dimensions,  and  the  S.A.E:  felloe  band  is  shrunk  over  it. 

Cast  steel  wheels  may  be  either  of  the  spoke  or  disc  type,  and 
both  seem  to  be  giving  good  results.  The  disc  type  either  have 
a  single  or  a  double  disc,  depending  upon  the  capacity,  while  the 
spoke  type  may  have  either  tubular  or  cross-section  spokes. 


MOTOR  TRUCK  WHEELS 


275 


The  single-disc  type  is  at  present  being  used  on  the  Nash  Quad 
Trucks,  and  this  application  is  clearly  shown  in  Fig.  261.  The 
essential  features  of  this  type  of  wheel  are  a  cast  hollow  box  sec- 


FIG.  261.     Nash  Quad  Cast-Steel  Wheel. 


FIG.  262.     Besco  Cast  Rear  Wheel  for  Dual  Tires. 

tion  rim  supported  by  a  curved  spring-like  section  to  struts  con- 
necting with  the  hub.  The  disc  includes  a  solid  cast  brake  drum 
and  container  for  the  driving  mechanism.  The  working  parts 


276    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


of  the  drive  are  thoroughly  protected  from  injury  by  the  wheel 
disc  and  brake  drum.  It  will  be  noted  that  the  hub  is  cast  in- 
tegral and  that  there  are  no  bolts  and  nuts  to  loosen  except  those 
which  retain  the  internal  gear. 


FIG.  263.     Spoke  Type  Cast-Steel  Front  Wheel. 

The  double-disc  type  for  heavier  vehicles  is  shown  in  Fig. 
262.  The  hub  and  brake  drum  are  cast  integral,  while  the  re- 
siliency is  obtained  through  a  wide  curvature  of  both  discs.  The 
rim  is  also  of  box-like  section,  however,  the  discs  extend  to  the 
hub  instead  of  forming  a  strut  at  the  bottom. 

Fig.  263  depicts  a  spoke  type  of  front  wheel  with  integral 
hub  and  rim;  There  are  eight  spokes  of  cross  section  thoroughly 
ribbed  and  fitted  to  obtain  the  greatest  possible  strength  with 
minimum  weight. 

Fig.  264  shows  this  type  of  rear  wheel;  however,  the  spokes 
are  of  Y-shape,  which  affords  a  greater  number  of  supports  to 
the  wheel  rim  without  increasing  weight,  and  enables  the  driving 
stresses  and  road  shocks  to  be  more  equally  distributed  over  the 
whole  wheel. 

Fig.  265  illustrates  the  hollow-spoke  type  of  wheel.  These 
spokes  are  of  tubular  section  and  are  connected  to  the  rim  by 
large  fillets.  The  hub  is  cast  integral,  wrhile  the  brake  drum  may 
be  cast  integral  or  bolted  to  this  type  of  wheel. 

Efforts  to  decrease  the  weight  of  steel  wheels  for  vehicles 
under  two-tons  capacity,  has  led  to  the  building  of  wheels  having 
the  disc  and  lighter  sections  of  the  wheel  made  of  pressed  steel, 
rigidly  connected  to  cast  steel  hubs. 


MOTOR  TEUCK  WHEELS 


277 


This  construction  is  shown  in  Fig.  266.  The  construction  is 
similar  to  the  cast  wheel  mentioned  above  with  a  box  type  hollow 
rim,  except  that  the  discs  are  flanged  a  little  deeper  at  the  rim  to 


FIG.  264.     Spoke  Type  Cast-Steel  Eear  Wheel. 


FIG.  265.     Hollow-Spoke  Type  Rear  Wheel. 

form  a  wider  box  section.  The  cast  flange  of  the  hub  is  carried 
out  further  to  carry  the  brake  drum  and  the  driving  mechanism. 
Wheel  construction  seems  to  be  one  of  the  principal  problems 
on  which  manufacturers  do  not  agree.  The  wheels  on  large  capa- 
city vehicles  to-day  are  called  upon  to  carry  a  very  heavy  burden 


278    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

at  higher  speed  than  ever,  and  they  must  also  stand  the  strain  due 
to  transmission  of  power.  In  order  to  meet  these  conditions,  the 
proportions  of  spokes  and  felloes  have  been  materially  increased, 
and  following  the  precedent  of  Europe,  cast  steel  wheels  are 
being  considered. 


FIG.  266.     Pressed  Steel  Eear  Wheel  for  Internal  Gear  Drive. 

Some  advantages  of  the  cast  wheel  have  been  outlined  above, 
while  of  course  it  possesses  certain  disadvantages.  However,  the 
steel  wheel  can  not  be  altered  for  different  types  and  sizes  of 
tires  as  easily  as  a  wood  wheel  and  a  spoke  in  a  wooden  wheel,  if 
broken  can  be  replaced;  but  in  this  event  the  entire  steel  wheel 
would  have  to  be  replaced.  Castings  are  always  liable  to  flaws 
and  blow  holes  and  it  is  difficult  to  secure  homogeneous  metal 
free  from  hard  spots.  Unequal  sections  cause  local  variations 
in  strength  and  internal  stresses  due  to  shrinkage  in  moulding. 
Where  numerous  cores  are  used  in  moulding,  it  is  difficult  to 
anchor  these  so  that  a  uniform  thickness  of  metal  can  be  ob- 
tained. Strains  due  to  shrinkage  can  be  eliminated  to  some  ex- 
tent by  heat  treating.  The  principal  argument  against  this 
wheel  is  that  under  severe  service  it  crystallizes;  however,  the 
design  of  this  type  of  wheel  is  of  such  nature  that  this  so-called 
difficulty  has  never  existed. 

A  steel  wheel  is  made  in  one  piece  and  can  be  arranged  to 
have  an  integral  brake  drum,  hub  and  flange,  and  there  is  no  op- 
portunity for  any  working  of  the  various  joints.  The  very 
nature  of  this  type  of  wheel  adapts  it  wonderfully  to  the  trans- 


MOTOR  TRUCK  WHEELS          279 

mission  of  power,  as  the  strength  lies  in  the  very  points  where 
the  driving  strains  are  centered. 

The  absolute  concentricity  of  the  hub,  sprocket  and  flange 
assist  greatly  in  the  economical  and  efficient  transmission  of 
power,  for  with  no  high  and  low  spots,  there  is  no  alternate 
tightening  and  loosening  of  the  chain.  In  shaft-driven  vehicles 
this  condition  is  even  more  important. 

Steel  wheels  also  possess  considerable  advantage  in  carrying 
dual  tires.  In  the  case  of  off- set  felloes,  the  outer  tire  is  entirely 
unsupported  by  the  spokes;  however,  in  this  case  the  steel  wheel 
is  particularly  valuable,  as  the  felloe  can  be  so  designed  that  the 
strains  on  the  outer  part  can  be  successively  transmitted  to  the 
spokes  or  discs  without  any  danger  to  the  wheel  itself.  Another 
feature  is  the  decreased  weight  at  the  rim  which  permits  more 
rapid  acceleration. 

The  advantage  of  obtaining  wheels  all  assembled  and  com- 
plete for  mounting  is  considerable.  No  division  of  responsibility 
exists  as  to  the  mounting  of  wheels  on  hubs,  brake  downs,  etc. 

Cast  steel  or  pressed  steel  wheels  can  be  and  are  made  to-day 
at  figures  competitive  with  wood  wheels.  If  the  demand  in- 
creases and  they  are  ordered  in  large  quantities,  the  cost  will  de- 
crease. In  considering  cost  it  should  be  remembered  that  the 
steel  wheel  has  the  hub  integral,  and  the  rear  wheel  may  also 
have  the  brake  drum  integral  and  the  cost  of  these  together  with 
all  bolts,  nuts,  felloe  band  and  the  labor  of  fitting  them  must  be 
added  to  the  wood  wheel  to  get  a  comparison  in  price. 

From  present  indications  it  appears  as  though  the  steel  wheel 
will  shortly  replace  the  wood  wheel  on  at  least  the  heavy  vehicles. 
The  demand  is  continually  increasing,  and  quite  a  number  of 
commercial  car  builders  are  experimenting  with  steel  wheels. 


CHAPTER  XXII 

MOTOR  TRUCK  TIRES  AND  RIMS 

IN  the  previous  chapters  considerable  has  been  mentioned 
about  tires  and  their  functions.  However,  in  this  chapter  the  con- 
struction of  a  motor  truck  tire  and  its  mounting  on  the  felloe 
band  of  the  wheel  will  be  described.  To  be  absolutely  efficient,  a 
commercial  car  must  be  able  to  carry  its  load  whenever  and 
wherever  needed.  The  vehicle  itself  may  be  as  nearly  as  possible 
absolutely  efficient,  when  measured  by  this  standard,  but  as  a 
whole  it  can  be  no  more  efficient  than  its  weakest  part.  Each  part 
must  be  so  designed  and  so  co-ordinated  with  other  parts  as  to 
perform  in  the  most  efficient  manner.  In  this  respect  the  tires 
are  no  exception. 

The  functions  which  the  tires  perform,  reduced  to  their  sim- 
plest terms,  may  be  listed  as  follows:  (1)  To  give  traction  to  the 
wheels  and  prevent  slipping,  (2)  to  protect  the  mechanism  of  the 
vehicle  from  jars  and  vibrations,  (3)  to  cushion  the  load. 

Tire  Development. — Before  the  advent  of  the  motor  truck, 
solid  rubber  tires  were  used  almost  exclusively  on  the  wheels  of 
carriages  to  provide  easier  riding.  On  these  vehicles  the  wheels 
were  merely  rolling  members  and  performed  no  tractive  effort,  as 
the  horses  did  the  pulling.  Such  tires  were  held  in  place  by 
means  of  wires  embedded  circumferentially  in  rubber,  the  whole 
unit  being  mounted  on  a  steel  channel  shrunk  on  the  felloe  of  the 
wheel.  These  tires  were  easily  applied,  but  possessed  certain  dis- 
advantages such  as  slipping  in  the  channel,  cutting  at  the  base 
and  release  of  the  rubber  adjacent  to  the  wires. 

This  type  of  tire  did  not  prove  very  satisfactory  for  heavy 
vehicles,  for  the  reasons  mentioned  above.  In  order  to  overcome 
these  shortcomings,  a  new  tire  was  introduced,  which  was  called 
the  side-wire'  type.  In  general  shape  and  appearance  it  was  the 
same  as  the  earlier  type.  However,  it  was  retained  in  the  chan- 
nel by  means  of  short  cross  wires  embedded  in  the  base  of  the  tire, 
which  projected  on  either  side.  These  cross  wires  were  held  in 
place  as  securely  as  possible  by  two  other  wires  running  circum- 
ferentially around  the  base  just  inside  the  edges  of  the  channel. 

280 


MOTOR  TRUCK  TIRES  AND  RIMS  281 

With  the  introduction  of  the  commercial  car,  an  entirely  new 
and  different  function  was  required  of  the  tires,  that  of  trans- 
mitting the  driving  power  from  the  rim  of  the  wheel  to  the  road 
surface,  i.e.,  the  tires  became  part  of  a  tractive  rather  than  a 
rolling  member.  Their  carrying  capacity  was  also  increased 
because  the  gasoline  engine  could  move  heavier  loads  than  the 
horse,  while  the  weight  of  the  truck  itself  was  considerably  more 
than  the  wagon,  and  the  speed  was  also  increased  considerably. 
The  carriage  type  of  tire  was  found  entirely  too  light  to  perform 
the  work  required  of  it.  This  condition  brought  about  the  inven- 
tion of  the  solid  motor  truck  tire,  a  tire  vulcanized  in  circular 
endless  form  to  fit  the  dimensions  of  the  wheel.  This  type  of  tire 
has  been  brought  out  in  different  designs  and  types  such  as  flange, 
internal  wire,  side  wire,  hard  rubber  and  metal-base  types,  also 
the  demountable. 

Carriage  tires  were  made  in  oval  shape,  in  cross  sections  from 
three-fourths  inch  and  of  compound  rubber  which  is  formed 
through  a  tubing  machine  die,  vulcanized  in  long  moulds  with 
many  cavities,  in  the  shape  in  which  it  had  been  designed. 

The  construction  of  solid  truck  tires  that  have  been  put  on 
the  market  is  very  similar  in  a  general  way.  The  rubber  is 
forced  through  a  die  or  tubing  machine,  or  built  up  from  sheets 
of  calendered  stock  in  endless  form  to  fit  the  exact  dimensions  of 
a  wheel  on  a  particular  style  of  base  or  retaining  body  of  the  tire 
as  designed  by  the  different  manufacturers,  according  to  their 
ideas,  which  have  taken  various  forms,  such  as  circumferential 
and  side  retaining  wires  which  are  engaged  over  embedded  cross 
wires,  bases  of  hard  rubber  in  various  forms  also  semi-hard 
rubber  which  can  be  moulded  into  the  tire  and  more  recently  the 
metal-base  type. 

This  tire  is  built  on  the  rim  at  the  factory  and  cannot  be  sep- 
arated from  it.  The  surface  of  the  metal  rim  is  cut  with  grooves, 
under  cut  notches  or  in  other  ways,  so  that  the  hard  rubber  gets 
a  firm  anchorage  into  the  rim.  In  manufacture  this  rubber  base 
is  applied  in  some  factories  in  layers,  just  as  you  wrap  a  bandage 
on  your  finger.  The  base  is  relatively  thin,  perhaps  not  one- 
eighth  the  radial  thickness  of  the  tire.  On  the  top  of  this  is  built 
the  regular  rubber  part  of  the  tire,  of  softer  rubber  to  afford  the 
desired  resilience.  This  part  is  also  in  some  factories  built  up 
similar  to  wrapping  a  bandage  until  the  desired  thickness  is  ob- 
tained, which,  when  done,  the  tire  is  trimmed  to  shape  and  vul- 
canized. 


282    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

Two  Metal-base  Types. — This  metal-base  tire  is  made  in  two 
types,  the  pressed-on  and  demountable.  In  the  larger  cities,  the 
former  is  quite  popular,  whereas,  in  the  smaller  outlying  cities 
and  towns  the  demountable  type  has  the  following.  The  reason 
for  this  is:  To  remove  a  pressed-on  tire  from  a  truck  wheel  or 
put  one  on  a  truck  wheel  requires  a  powerful  press,  which  means 
a  considerable  outlay  to  the  dealer  in  proportion  to  the  amount 
of  work  he  may  get. 

The  demountable  tire  can  be  removed  from  the  wheel  and  a 
new  one  fitted,  without  the  truck  owner  having  to  take  it  to  a 
garage.  Unfortunately  it  is  more  expensive  than  the  pressed-on 
tire,  due  to  the  forged  and  rolled  steel  parts  used  with  it. 

Rubber. — Crude  rubber  is  a  vegetable  product  gathered  from 
certain  species  of  tropical  trees,  shrubs,  vines  and  roots.  It  was 
first  used  for  pencil  erasers  and  in  waterproof  cloth  and  finally 
in  solution  in  cements.  Vulcanizing  or  curing  rubber  was  dis- 
covered in  1844;  thereafter  the  development  of  the  industry  was 
rapid,  though  it  was  but  an  infant  in  size,  compared  with  now, 
up  to  the  development  of  the  automobile  industry. 

There  are  many  kinds  and  grades  of  rubber,  and  these  may  be 
divided  into  two  classes,  wild  and  cultivated. 

Wild  Rubber. — This  is  collected  from  trees  that  have  grown 
wild  and  where  there  has  been  no  cultivation  process.  Such 
trees  and  shrubs  are  found  mostly  in  Northern  South  America, 
Central  America  and  Central  Africa.  Fine  Para  comes  from 
the  Amazon  region  of  South  America.  For  over  a  century  this 
rubber  has  been  gathered  in  practically  the  same  way.  The 
native  goes  into  the  forest,  selects  a  tree,  cuts  V-shaped  grooves 
in  herring-bone  fashion  around  the  tree,  with  one  main  groove 
down  the  center  like  the  main  vein  in  a  leaf.  The  latex  of  the 
tree  (not  the  sap)  flows  from  the  smaller  veins  and  down  the 
center  vein  into  a  little  cup  placed  to  receive  it. 

When  full  these  cups  are  gathered  and  brought  into  the  rubber 
camp,  and  there  the  latex  is  coagulated  by  means  of  smoke. 
This  is  done  by  the  use  of  a  paddle,  which  is  alternately  dipped 
into  a  bowl  of  latex  and  then  revolved  in  the  smoke  which  seems 
to  have  a  preservative  effect  on  the  rubber  as  well  as  drying  it 
out  and  causing  it  to  harden  on  the  paddle,  each  successive  layer 
of  latex  causing  the  size  of  the  rubber  ball  or  biscuit  to  increase. 
When  a  biscuit  of  sufficient  size  has  been  coagulated  it  is  re- 
moved from  the  paddle  and  is  ready  for  shipment.  There  are 


MOTOE  TRUCK  TIKES  AND  RIMS  283 

other  grades  of  rubber  which  are  coagulated  by  adding  some 
alkaline  solution  and  allowing  it  to  dry  out.  Central  America 
produces  a  grade  of  rubber  which  is  cured  by  being  mixed  with 
juices  which  are  obtained  by  grinding  up  a  certain  plant  which 
grows  in  that  district. 

In  Central  Africa  some  of  the  rubber  is  gathered  from  trees, 
but  most  of  it  comes  from  vines  and  roots,  and  the  methods  of 
coagulation  are  varied.  Practically  all  of  them  are  dried  out  in 
the  sun. 

Cultivated  Rubber. — Cultivated  rubbers  are  obtained  from 
East  India,  Ceylon,  Malayan  Peninsula  and  southern  Mexico. 
The  claim  is  made  that  the  best  of  these  is  the  Ceylon  rubber, 
which  has  been  grown  from  sprouts  taken  from  the  wild  Para 
trees  of  South  America.  These  cultivated  trees  have  been  very 
carefully  reared  and  scientific  methods  used  in  tapping  them,  so 
as  not  to  in  any  way  hurt  the  bearing  qualities  of  the  tree.  This 
product  is  very  uniform,  as  very  scientific  methods  are  used, 
coagulating,  drying  and  otherwise  treating  the  rubber  before  it 
leaves  the  plantation,  so  that  there  is  a  minimum  deterioration 
due  to  oxidation  and  other  actions  during  the  time  the  rubber  is 
en  route  from  the  plantation  to  the  manufacturer.  Of  late,  far 
east  rubber  is  being  given  the  preference,  because  it  is  cleaner 
and  contains  less  foreign  matter  than  the  wild  para. 

Manufacturing  Process. — This  rubber  as  it  comes  into  the 
market,  contains  a  lot  of  impurities,  and  before  it  can  be  used  it 
has  to  be  washed.  This  washing  is  done  between  rolls  which  are 
grooved  to  tear  the  rubber  apart,  water  being  fed  on  the  rolls  to 
wash  off  all  foreign  matter.  In  this  process  the  rubber  loses 
considerable  of  its  weight. 

When  the  rubber  is  washed  and  dried  it  is  mixed  with  chem- 
icals and  into  a  compound.  These  chemicals  and  particles  of 
rubber  are  placed  in  metal  boxes  a  couple  of  feet  square.  The 
formula  for  these  compounds  are,  of  course,  kept  secret  by  the 
rubber  factories,  because  they  represent  the  outcome  of  very  long 
and  tedious  experiments  which  are  looked  upon  as  one  of  the 
chief  assets  of  any  rubber  mill.  These  masses  of  compounds  are 
chewed  and  rechewed,  ground  and  reground,  extenuated  and  re- 
extenuated,  between  the  giant  steel  rolls  of  the  calendering  ma- 
chines that  are  needed  just  to  thoroughly  mix  the  ingredients. 
Each  compound  requires  its  separate  mixing,  its  special  treatment. 


284    MOTOE  TEUCK  DESIGN  AND  CONSTEUCTION 

The  rims  to  which  the  hard  rubber  is  vulcanized  are  in  most 
cases  copper  plated,  as  rubber  compounds  do  not  take  kindly  to 
steel.  The  hard  rubber  base  is  applied  to  the  metal  rim  and  then 
the  tire  is  completed  as  previously  mentioned. 

The  compound  rubber  is  in  graduated  consistencies  from  the 
hard  rubber  base,  which  forms  the  inside  circumference  next  to 
steel  base,  to  the  resilient  rubber  forming  the  wearing  part  of 
the  tire. 

When  the  tire  is  completed  it  is  pressed  into  moulds  which 
are  securely  bolted  and  placed  in  large  cylindrical  vulcanizers 
which  vulcanize  or  cure  the  rubber.  When  this  process  has  been 
completed  and  the  tires  have  cooled,  slight  edges  remain  which 
are  buffed  off. 

Rims.  —  Tire  rims  or  metal  bases  and  felloe  bands  are  usually 
made  from  flat  stock  and  rolled  to  shape,  and  the  ends  are 
welded  together.  Special  machinery  is  used  for  this  purpose  and 
each  band  or  base  must  check  within  certain  limits.  Demount- 
able rim  parts  are  made  in  a  similar  manner  and  must  also  be 
held  within  certain  limits. 

The  Solid-truck  Tire.  —  A  number  of  illustrations  are  shown 
herewith,  which  give  the  contour  and  general  construction  of  the 
solid  tire.  The  Firestone  wired-on  tire  is  made  and  recommended 
for  use  on  light  vehicles  only.  This  tire  is  not  manufactured 
into  the  rirn  as  is  the  hard  rubber  base  type,  but  is  afterwards 

attached  to  the  rim.     Into 


CROSS  WIRE      placed  stout  cross  wires  at 
-FLANGE          frequent  intervals.     When 
-BOL  T  this  tire  is  placed  on  a  chan- 

FELLOE  BAND    nel  rim  it  is  held  in  place  by 
FELLOE  two   circumferential  wires, 

FIG.  267.   Eepublic  Side-Flange  Type  Tire,  one  at  each  side  of  the  tire, 

these    wires    resting    upon 

the  ends  of  cross  wires,  by  virtue  of  which  the  tire  is  retained  on 
the  rim.  Swinehart  manufactures  what  is  called  a  soft-base  tire, 
with  cross  wires  for  holding  it  in  the  channel  rim.  Several  other 
makers  also  manufacture  tires  which  are  retained  by  cross  or  cir- 
cumferential wires. 

The  hard  rubber  base  tire  as  previously  mentioned  is  built 
onto  the  rim  at  the  tire  factory.  This  type  of  tire  is  being  made 
by  Goodrich,  Firestone,  Goodyear,  United  States,  Eepublic, 


MOTOR  TRUCK  TIRES  AND  RIMS 


285 


JIRERIM 


Kelly- Springfield,  Gibney,  Swinehart,  Hood,  Polack,  etc.,  in  the 
single  and  dual,  pressed-on  and  by  some  in  the  demountable 
types,  some  of  which  are  il- 
lustrated. 

These  various  makes  dif- 
fer in  the  contour  of  the  tire, 
the  method  of  producing  a 
firm  grip  for  the  hard  rubber 

on  the  steel  and  the  method       FIG  26g     Republic  pressed-on  Type 
of  building  up  the  tire,  while  Tire, 

the    demountables   differ   in 

rim  construction.  In  some  cases  the  metal  base  is  cut  in  dove- 
tail fashion  and  with  grooves,  such  as  the  Hood,  Polack  and 
Goodrich.  In  the  Gibney  and  Kelly,  the  hard  rubber  is  car- 
ried up  to  the  side  of  the  metal  base,  while  in  others  it  is  set 
straight  across  the  width  of  the  channel  base.  In  some  cases  the 


FIG.  269.     Goodrich  DeLuxe  Pressed-on  and  Demountable  Types. 

layer  of  hard  rubber  is  given  an  irregular  wave  line  surface  such 
as  the  Goodrich  in  order  to  increase  the  area  of  contact  between 
the  two  grades  of  rubber. 


EUROPEAN  TYPE  AMERICAN  TYPE 

FIG.  270.     Polack  Pressed-on  Type  Tire. 

The  metal  base  or  rim  of  a  demountable  tire  has  the  inner  cir- 
cumference tapered  from  both  sides,  its  smallest  diameter  being 
slightly  larger  than  the  outside  diameter  of  the  felloe  band. 
Rings  which  have  a  tapered  surface  and  are  usually  termed 


286    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

wedge  rings,  since  their  cross  section  is  of  wedge  shape,  are  in- 
serted between  the  felloe  band  and  the  tire  base.  These  are  re- 
tained by  circular  flanges  and  bolts  which  pass  through  these 
and  the  felloe  of  the  wheel. 


CENTER  WEDGE  PI NG^ 


FIG.  271.     Kelly-Springfield  Demountable  Type  Single  and  Dual. 

Most  tire  manufacturers  use  this  construction;  however,  the 
Goodrich  demountable  differs  somewhat  in  that  the  wedge  section 
is  incorporated  in  the  tire  base  against  which  the  side  flanges 
press.  The  rubber  portion  of  a  solid  tire  is  usually  about  2J  ins. 
high  and  varies  in  width  according  to  its  design.  This,  of  course, 
governs  the  elasticity  and  cushioning  effect.  On  the  large  single 
tires,  this  height  does  not  give  a  proper  proportioning  and  to 
overcome  this  some  makers  produce  what  is  commonly  called  the 


CENTER  VYEOGE  RiHG 


FIG.  272.     Goodyear  Demountable  Type  "  SV "   Single  and  Dual. 

European  type  of  tire,  in  which  the  rubber  is  from  \  to  1  in. 
higher.  The  Goodrich  Co.  calls  this  their  De  Luxe  type  and 
while  it  is  designed  after  the  European  type,  it  has  quite  a  dif- 
ferent contour.  Greater  resilience  is  claimed  for  these  types  as 
well  as  longer  life  and  greater  load  carrying  capacity.  A  greater 
carrying  capacity  is  possible,  because  the  contact  with  the  road 


MOTOR  TRUCK  TIRES  AND  RIMS 


287 


surface  is  much  larger,  consequently  the  weight  is  distributed 
over  more  base  area.  The  greater  height  of  rubber  and  increased 
resiliency  also  give  an  entirely  different  traction  hold  on  the  road. 


CHANNEL  RIM 
RUBBER 
CROSS  WIRE 

CIRCUMFERENTIAL  WIRE 
FELLOE  BAND 


RUBBER 
HARDRUBB5P 
TIRE  RIM 
WEDGE  RING 
FLANGE 

BOLT 
FELLOE  BAND 

FELLOE 


EUROPEAN 
SED-O 


WIRED-ON 
TYPE 


DEMOUNTABLE 


FIG.  273.     Firestone's  Variety   of   Solid  Tires. 


Some  tire  makers  recommend  this  type  of  tire  as  an  oversize  for 
the  American  type,  since  it  is  made  to  fit  the  S.A.E.  standard 
felloe  bands. 

The  Goodrich  Co.  has  recently  introduced  a  new  policy  with 
regard  to  single  and  dual  tires  for  heavier  truck  work.     This 


FIG.  274.     Goodyear  Pressed-on  Type  "  SU  "  Single  and  Dual. 

company  is  recommending  a  7-in.  single  in  preference  to  4-in. 
duals  and  6-in.  singles  in  preference  to  3J-in.  duals.  The  argu- 
ments are  that  these  singles  give  better  results  than  the  corre- 
sponding duals,  in  that  often  on  the  road  one  of  the  duals  has  to 


288    MOTOR  TKUCK  DESIGN  AND  CONSTRUCTION 

take  the  entire  weight  of  the  load  on  that  wheel  and  that,  as  it  is 
not  designed  to  take  the  entire  load,  it  is  naturally  overloaded 
and  perhaps  permanently  injured  by  this  frequent  caring  for  the 


RUBBER 
HARO  RUBBER 


EUROPEAN  SECTION          AMERICAN  SECTION 

FIG.  275.     Hood  European  and  American  Section  Pressed  Type  Tires. 

entire  load  weight  on  one  wheel.    With  singles  this  is  not  the  case. 

Firestone  has  recently  introduced  what  is  known  as  a  giant 

single  solid  tire  made  in  8-  or  12-in.  width.    The  extra  amount 


FIG.  276.     Kelley-Springfield    Pressed-on   Type    Single    and   Dual. 

of  rubber  is  claimed  to  make  it  oversize  equipment  for  6-in.  duals 
and  equal  equipment  for  7-in.  duals.  The  tread  has  three  evenly 
spaced  circumferential  grooves  in  it. 

The  Hood  Co.  recommends  its  European  type  of  tire  for  dual 
equipment,  as  they  claim  this  type  with  its  greater  resiliency  will 


FIG.  277.     Gibney  Wireless  Type  "  MIB  "  Pressed-on. 

alloV  the  inside  tire  to  compress  more  and  allow  the  outside  tire 
to  take  its  share  of  the  load. 

The  pressed-on  tire  will  no  doubt  gain  in  popularity  as  it  is 
less  expensive  than  the  demountable  type,  since  wedge  rings, 


MOTOR  TRUCK  TIRES  AND  RIMS  289 

flanges  and  bolts  are  eliminated,  while  the  firm  fit  to  the  wheel 
also  insures  the  greatest  possible  mileage.  Practically  all  makers 
are  continuing  their  demount  ables,  but  the  number  produced  is 
on  the  wane.  This  type  will  no  doubt  be  continued  for  some  time 
since  powerful  hydraulic  presses  the  cost  $500  to  $700  are  re- 
quired to  apply  the  pressed-on  type.  This,  of  course,  is  a  consid- 
erable outlay  for  a  dealer  in  proportion  to  the  work  he  may  get 
at  present.  However,  the  demand  for  trucks  is  continually  in- 
creasing and,  in  order  to  assist  the  dealer  in  obtaining  his  share 
of  the  business,  some  tire  companies  are  selling  these  presses  at 
the  rate  of  $100  down  and  $100  per  year  until  paid  for,  on  condi- 
tion that  it  is  used  only  in  connection  with  tires  made  by  that 
company. 

The  claim  made  for  the  European  type  of  tire  is  that  owing 
to  its  higher  section  and  greater  resiliency  it  greatly  reduces  the 
cost  of  upkeep  of  the  mechanism  of  the  truck,  and  makes  it  far 
more  comfortable  for  the  driver. 

The  Care  of  Motor-truck  Tires. — The  care  of  the  mo  tor- truck 
tire,  while  an  important  item  in  the  maintenance  of  a  commercial 
vehicle,  is  not  generally  understood  by  operators  of  these  vehicles. 
All  manufacturers  of  solid  rubber  tires  issue  instruction  books 
or  cards  on  this  subject,  but  these,  like  most  all  other  instruction 
books,  find  their  way  into  the  tool-box  and  remain  there  until 
trouble  arises.  Tire  makers,  however,  are  endeavoring  to  edu- 
cate operators  on  this  subject,  and  since  very  little  mention  has 
been  made  regarding  this,  the  writer  will  endeavor  to  cover  it  in 
such  manner  as  to  enable  the  layman  to  become  familiar  with  the 
attention  tires  require,  to  give  maximum  mileage. 

There  have  been  many  refinements  in  the  construction  of 
motor-truck  tires,  and  the  majority  are  very  dependable;  but 
tires,  like  the  engine,  transmission,  axles  and  all  other  parts  of 
the  vehicle,  must  have  a  reasonable  amount  of  attention  if  one 
expects  to  obtain  the  best  results.  Tire  equipment  is  given  care- 
ful consideration  by  the  engineer  and  the  tire  maker  in  deter- 
mining the  necessary  sizes  and  types.  However,  no  provision 
can  be  made  for  the  usage  of  the  vehicle  or  the  care  of  the  tires. 
Provision  is  made  for  taking  up  wear  and  alignment  in  the 
mechanical  parts  of  the  chassis  which  affect  the  life  of  the  tires. 
However,  these  are  not  automatic  adjustments,  and  require  fre- 
quent inspections.  Tires,  like  all  other  parts,  have  a  physical 
limit,  and  results  can  only  be  obtained  if  their  usage  is  within  the 

20 


290    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 

limits  of  their  physical  strength,  which  is  based  upon  the  com- 
pression of  the  vulcanized  rubber. 

For  maximum  tire  mileage,  three  factors — the  tire,  the  road 
and  the  driver — must  be  considered.  The  tire  must  be  consid- 
ered because  the  type  of  tire  used  for  quick  delivery  cannot  be 
used  for  heavy  duty.  The  road  naturally  effects  the  mileage  of 
truck  tires,  because  the  bumps  and  ruts  of  bad  roads  throw  local- 
ized shocks  on  them.  The  driver,  next  to  the  tire  itself,  is  the 
most  important  factor.  It  depends  upon  him  whether  the  truck 
be  abused. 

In  the  following  an  outline  of  the  common  injuries  to  motor- 
truck tires  is  given,  most  of  which  are  sustained  in  running,  and 
may  be  traced  directly  to  one  of  the  three  factors  mentioned 
above.  These  common  injuries  may  be  summed  up  as  follows: 
Overloading,  speeding,  rough  roads,  wheel  alignment  and  irregu- 
larities, anti-skid  devices,  neglected  cuts,  skidding  and  applica- 
tion of  brakes,  application  of  power,  running  in  car  tracks,  heat, 
oil  and  grease  and  abuse  of  trailers. 

The  most  premature  tire  failures  are  due  to  overloading,  not 
only  by  constant  overloading,  but  by  the  momentary  overload- 
ing as  well.  Rubber,  like  any  other  material,  has  its  limits  of 
resistance,  this  resistance  being  its  ability  to  return  to  its  original 
shape  after  being  compressed.  This  may  be  compared  with  an 
ordinary  rubber  band,  which  will  snap  if  stretched  beyond  its 
limit  of  elongation,  as  the  rubber  in  a  motor-truck  tire  will  snap 
at  once,  even  though  momentarily  loaded  beyond  its  limits  of 
compression.  This  compression  is  noticeable  by  the  bulging  out 
of  the  rubber,  both  left  and  right  and  even  front  and  rear.  If 
the  load  is  within  the  capacity  of  the  tire  the  rubber  will  with- 
stand the  strain  and  as  the  load  is  released,  return  to  its  original 
shape,  the  same  as  a  rubber  band  when  stretched  and  released. 
However,  if  the  load  is  beyond  the  capacity  of  the  tire  the  rubber 
will  break  down  as  inevitable  as  when  stretched  beyond  its  limit 
of  elongation.  If  the  tire  is  overloaded  momentarily  the  rupture 
may  not  be  apparent,  as  the  broken  portions  may  be  hidden  by 
others  not  noticeably  affected,  yet  the  strength  of  the  tire  is  im- 
paired and  failure  of  the  whole  structure  is  merely  a  matter  of  a 
short  time,  as  the  damage  is  bound  to  spread. 

The  distribution  of  the  load  also  has  an  important  bearing 
upon  the  life  of  a  tire,  as  trucks  are  frequently  loaded  so  that  the 
heavy  articles  are  carried  near  the  tail-board,  while  the  forepart 
of  the  body  carries  little.  In  this  case  the  rear  tires  usually 


MOTOR  TRUCK  TIRES  AND  RIMS 


291 


carry  an  overload,  although  the  total  load  may  be  within  the 
capacity  of  the  vehicle.  Loads  which  overhang  the  rear  of  the 
body,  such  as  lumber,  pipes,  etc.,  also  produce  the  same  effect. 
It  does  not  matter  whether  the  overload  is  a  constant  one  or  a 
momentary  one  as  far  as  the  cause  of  the  damage  is  concerned, 
and  is  only  material  to  the  extent  of  the  damage.  A  momentary 
overload  may  have  ruptured  the  tire  structure  only  in  a  single 


FIG.  278.     Overloaded,  Overspeeded  and  Bad  Road  Tire  Effects. 

spot,  whereas  a  constant  overload  will  damage  the  whole  tire, 
thus  hastening  it  to  complete  failure;  but  in  both  cases  the  tire 
is  doomed  to  premature  ruin. 

Small  dual  tires  are  often  exposed  to  momentary  overloads, 
as  the  camber  of  the  road  may  be  such  as  to  throw  the  total 
weight  alternately  on  one  of  the  outer  or  inner  tires,  the  mates 
being  momentarily  relieved  of  their  load. 

Speeding. — A  tire  which  is  overspeeded  is  prematurely  de- 
stroyed in  a  manner  very  similar  to  that  of  an  overloaded  tire. 
Overspeeding  makes  every  road  rough,  because  it  magnifies  every 


292    MOTOR  TKUCK  DESIGN  AND  CONSTRUCTION 

irregularity  and  this  increases  the  effect  of  all  shocks.  Hitting 
a  curb,  bump  or  any  other  obstacle  with  considerable  impetus, 
even  though  the  truck  be  empty,  is  in  effect  identical  with  a 
momenary  overload,  causing  a  rupture  in  the  rubber  structure 
in  that  particular  spot  and  gradual  ruin  of  the  tire,  for  as  the 
wheel  revolves  at  excessive  speed  the  rapidity  of  compression 
and  expansion  of  the  rubber  generates  internal  friction  heat. 
This  is  increased  considerably  by  the  friction  of  the  road,  thus 
heating  the  rubber  to  a  higher  degree  than  it  can  resist.  This 
combined  with  the  increased  effect  of  all  shocks  is  very  de- 
structive. 

Rough  Roads. — Rough  roads  have  an  effect  on  solid  rubber 
tires  similar  to  that  of  overloading  and  overspeeding,  as  the  face 
of  the  tire  rests  successively  on  irregularities  which  have  the 
effect  of  overloading  that  particular  portion  of  the  tire.  These 

irregularities,  such  as  ruts, 
large  stones,  crushed  stone, 
loose  brick  and  similar  road 
materials,  cause  shocks 
which  tax  the  tires  beyond 


^      _„_     _,  the  limit  of  their  power  to 

FIG.  279.     Front  Wheels  out  of  Line 

due  to  Striking  Curb  or  Obstacle  on  the      absorb  them  and  these  m°- 
Eoad.  mentary  overloads  create  a 

disintegrating  effect  upon 

the  tread  of  the  tire.  Some  roads  have  an  extreme  heat  which 
also  causes  disintegration  while  others  produce  a  similar  effect, 
owing  to  their  composition.  Careful  driving  over  rough  roads  at 
moderate  speed,  avoiding  ruts,  stones  and  loose  surface  material  as 
much  as  possible,  will  greatly  increase  tire  mileage. 

Wheel  Alignment  and  Irregularities. — Any  fault  in  align- 
ment allowing  the  wheels  to  run  out  of  parallel  no  matter  to  what 
small  extent  prevents  their  true  rolling  motion.  When  two  op- 
posite wheels  are  not  parallel  there  is  a  diagonal  grind  upon 
these  at  the  point  where  they  come  in  contact  with  the  road  sur- 
face. This  grinding  action  quickly  wears  off  the  rubber,  the  wear 
being  very  smooth  just  as  though  the  rubber  had  been  ground 
off  on  an  emery  wheel. 

Misalignment  of  wheels  generally  is  evidenced  through  ex- 
cessive wear  on  one  side  or  by  flats,  as  these  when  once  started 
rapidly  develop.  There  are  a  number  of  things  which  affect  the 
alignment  of  front  wheels.  The  cross  rod,  axle,  or  steering 


MOTOK  TRUCK  TIRES  AND  RIMS 


293 


knuckle  may  be  bent  due  to  violent  contact  with  the  curb,  another 
vehicle  or  obstacle,  the  cross-rod  or  knuckle  may  be  improp- 
erly    adjusted,    loose    or      _____ 
worn    hubs,    bearings    in 
the  wheels  and  bushings 
in    the    steering    linkage 
may  be  worn,  or  the  ad- 
justments may  have  been        Fm  280    Front  Wheels  Qui  of  Line  due 

disturbed    through    vibra-  to  Wear   or   Improper  Adjustment. 

tion. 

All  wheels  should  be  frequently  tested  for  alignment  and 
always  after  a  collision  or  untoward  event  that  is  likely  to  effect 
the  wheel  adjustments.  A  piece  of  tubing  fitted  with  a  sliding 
rod  and  a  thumb  screw,  or  a  stair  tread  extension  rule,  form  a 
useful  gage  for  front  wheel  testing.  In  testing  front  wheels  it 
is  most  important  that  the  dead  vertical  center  is  measured,  both 
front  and  rear.  This  is  necessary  because  of  the  tendency  of  the 
front  wheels  to  spread  under  the  driving  force  and  it  is  the  prac- 
tice of  commercial  vehicle  builders  to  set  the  front  wheels  at  a 
toe  in  from  one-fourth  to  five-eighths  in.  less  in  front  of  the 
axle  than  in  back  of  it.  This  allows  one-eighth  in.  to  five-six- 
teenth in.  toe  in  for  each 
front  wheel.  This  is 
practically  taken  out  by 
the  action  of  the  vehicle 
on  the  road,  for  under 
momentum  the  wheels 
will  be  approximately 
parallel. 

Each  wheel  can  also  be  checked  up  separately  by  raising  it 
with  a  jack  and  placing  a  stationary  point  almost  against  the 
wood  felloe.  Revolving  the  wheel  will  determine  if  the  distance 
between  the  stationary  point  and  the  felloe  is  the  same  at  all 
points  around  the  wheel.  If  the  wood  felloe  rubs  at  some  point 
around  and  not  at  other  places  it  may  be  due  to  a  slight  varia- 
tion in  the  felloe,  but  more  usually  it  is  the  result  of  a  wheel  not 
running  true. 

Irregularities  of  the  driving  wheels  of  a  motor  vehicle  do 
not  exist  to  the  extent  that  is  the  case  with  the  front  wheels, 
though  it  occasionally  occurs  that  when  the  rear  axle  is  displaced 
to  one  side  or  the  other  it  causes  the  wheels  to  take  up  a  diagonal 


FIG.  281.     Eear  Axle  out  of  Alignment 
due  to  Poor  Chain  Adjustment. 


294    MOTOE  TRUCK  DESIGN  AND  CONSTRUCTION 

position  with  a  consequent  grinding  action  upon  the  tires.  It  is 
essential  should  it  be  discovered  that  these  are  out  of  parallel 
that  the  trouble  be  rectified  immediately.  For  testing  rear 
wheels,  both  comparatively  and  their  relation  to  the  front  wheels, 
the  ordinary  line  and  rod  method  cannot  be  improved  upon. 
The  measurement  between  the  wood  felloes  of  the  rear  wheels 
should  be  the  same  both  in  front  and  rear  wheels  of  the  axle. 
Whenever  an  undue  amount  of  play  is  discovered  in  the  wheels 
steps  should  be  immediately  taken  to  remedy  the  defect,  other- 
wise irreparable  damage  to  the  tires  is  inevitable. 

Anti-skid  Devices. — Anti-skid  devices,  especially  those  which 
are  stationary  upon  the  wheel,  contribute  a  great  deal  toward 
causing  solid  rubber  tires  to  give  unsatisfactory  service.  The 
loose  chain  is  by  far  the  least  injurious  as  it  will  work  its  way 
around  the  tire  and  equally  distributes  the  Avear  and  strain. 
However,  with  a  stationary  chain  this  is  constantly  confined  at 
the  point  of  bearing. 

These  anti-skid  devices  are  mostly  applied  to  the  driving  or 
rear  wheels  of  a  vehicle  and  these  are  quite  apt  to  spin  in  slip- 
pery places,  causing  sharp  blows  at  the  points  of  contact.  With 
a  sationary  device  the  shock  received  by  the  tires  in  striking  the 
ground  is  concentrated  in  a  few  points  around  its  circumference, 
causing  heavy  strains  at  these  points.  In  order  to  avoid  this,  de- 
vices having  numerous  cross-pieces  should  be  used  for  as  the  dis- 
tance between  these  is  decreased  the  force  of  the  blow  decreases 
as  the  wheel  gains  momentum.  Every  type  of  anti-skid  device  is 
more  or  less  injurious  to  the  tire  and  they  should  only  be  used 
temporarily  to  pass  over  soft  slippery  places. 

Neglected  Cuts. — Cuts  are  of  common  occurrence  and  are  gen- 
erally caused  by  road  conditions.  These  cuts,  no  matter  how 
small,  afford  an  entering  place  for  sand  and  fine  gravel,  causing 
the  cut  to  increase  in  length  and  depth.  Sand,  gravel  and  other 
gritty  substances  are  enemies  of  rubber  and  once  they  effect  an 
entry  into  the  tires  it  is  pretty  hard  to  combat  them.  Cuts  near 
and  at  the  edges  are  most  injurious,  and  if  attended  to  in  time 
are  easily  remedied.  These  should  be  trimmed  off  smoothly  with 
a  sharp  knife  as  soon  as  they  occur,  and  if  they  are  not  trimmed 
the  revolving  wheel  causes  the  loosened  edges  to  catch  on  every 
obstruction,  so  .that  the  tear  constantly  increases.  When  one 


MOTOR  TRUCK  TIRES  AND  RIMS  295 

unit  of  a  dual  tire  is  permitted  to  weaken  in  this  manner  it  causes 
an  overload  on  its  mate. 

Skidding  and  Application  of  Brakes. — Skidding  is  generally 
caused  by  sudden  application  of  the  brakes,  turning  corners  too 
rapidly  and  turning  corners  so  small  that  the  crown  of  the  road 
may  cause  the  rear  wheels  to  skid.  The  effect  of  skidding  or  lock- 
ing the  wheels  is  quite  serious,  as  this  causes  flats  on  the  tread 
of  the  tires,  in  addition  to  placing  the  tires  under  side  strains, 
which  tears  them  loose  from  the  base.  This  same  condition  will 
also  exist  if  the  brakes  do  not  grip  evenly,  causing  one  wheel  to 
roll  while  the  other  drags.  Turning  corners  too  rapidly  increases 
strain  and  wear  on  the  tires  with  a  similar  effect.  Some  tire 
makers  recommend  truing  up  tires  if  flats  develop,  by  turning 
down  the  tread,  otherwise  these  will  develop  rapidly  and  cause  a 
great  loss  of  mileage. 

The  sudden  application  of  power  by  quick  engagement  of  the 
friction  clutch  produces  the  same  effect  as  locking  the  wheels. 
The  power  applied  at  the  hub  starts  the  rim  first  and  the  re- 
sistance of  the  road  prevents  the  tire  from  starting  at  the  same 
instant.  This  brief  delay  slightly  stretches,  displaces  or  strains 
the  rubber,  just  as  the  life  is  taken  out  of  a  rubber  band  by  con- 
tinual stretch.  This  danger  is  greatly  augmented  as  wear  takes 
place  in  the  driving  members,  such  as  the  hubs,  universal  joints, 
driving  chains,  etc. 

Running  in  Car  Tracks. — Injuries  resulting  from  running  in 
car  tracks  are  serious  and  readily  apparent.  Under  this  condi- 
tion, the  outside  edge  of  the  tire  rests  .upon  the  raised  edge  of  the 
car  track,  so  that  the  distribution  of  the  load  is  on  but  a  small 
portion  of  the  tire.  That  is,  the  weight  of  the  vehicle  is  being 
supported  by  that  small  portion  of  the  tire  which  is  riding  on 
the  raised  part  of  the  track.  Throwing  the  load  upon  half  of 
the  tire  causes  it  to  wear  rapidly,  while  the  rest  of  it  is  in  ap- 
parently good  condition.  With  dual  tires  this  effect  is  still  more 
pronounced  because  that  part  of  the  unit  riding  on  the  car  track 
must  sustain  the  load  intended  for  both  tires. 

Heat  causes  disintegration  of  the  rubber.  In  winter  the  large 
garages  are  generally  heated  by  steam,  the  headers  of  which  are 
fastened  close  to  the  ceiling  of  the  floor  below.  This  heats  the 
floor  above  to  quite  an  extent,  and  if  a  heavy  truck  is  parked  for 
two  or  three  days  directly  over  a  big  hot  spot  in  the  floor  a  con- 


296    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


dition  is  developed  that  results  in  a  flat  being  formed  in  the  tire 
shortly  afterwards.  This  is  due  to  the  action  of  the  heat  soften- 
ing the  rubber,  while  the  weight  of  the  truck  is  resting  upon  it, 
causing  a  flow  that  never  fully  returns. 

Gasoline,  oil,  grease  and  other  fatty  substances  are  solvents 
of  rubber.  If  garage  floors  are  not  kept  clean  and  the  tires  stand 
in  a  pool  of  oil,  a  similar  action  to  that  of  the  effect  of  heat  will 
take  place.  Grease  and  oil  can  easily  be  removed  by  a  rag  satu- 
rated with  gasoline.  Gasoline,  although  a  solvent,  evaporates 
quickly  and  if  applied  in  small  quantities  will  not  cause  any  in- 


FIG.  282.     Tires   Showing  Undue  Wear. 

jury  if  used  as  a  cleansing  agent.  Another  difficulty  occurs  in 
the  abuse  of  trailers,  which  is  caused  by  turning  too  sharp  a 
corner  while  loaded.  The  effects  of  this  are  similar  to  those 
caused  by  skidding,  as  it  tends  to  wrench  the  inside  wheel,  twist- 
ing the  tire,  which  is  firmly  held  to  the  road  by  the  weight  of  the 
load.  The  results  are  a  loose  tire  in  a  very  short  time. 

The  above  gives  the  general  abuse  of  commercial  vehicle  tires, 
and  while  there  are  numerous  others  of  minor  importance,  it  has 


MOTOR  TRUCK  TIRES  AND  RIMS  297 

been  proven  by  maintenance  engineers  that  many  tire  miles  can 
be  saved  by  avoiding  the  above  sources  of  trouble.  In  order  to 
obtain  maximum  tire  mileage,  commercial  vehicle  owners  should 
instruct  operators  to  avoid  all  overloads,  momentary  ones  as  well 
as  constant  ones,  speeding,  curbs,  ruts,  car  tracks  and  reckless 
backing  up  against  curbs,  and  also  to  properly  distribute  the  load 
and  to  select  the  best  roads  and  smoothest  pavements. 

Truck  operators  can  save  a  considerable   amount  by  using 
judgment  in  the  operation  of  a  commercial  vehicle. 


CHAPTER  XXIII 

ELECTRIC  LIGHTING  AND   STARTING  ON  COMMERCIAL  TRUCKS 

The  Advantages  and  Disadvantages  of  Electrically  Equipped 
Trucks. — Is  electric  lighting  and  starting  equipment  justifiable 
on  commercial  cars?  Many  engineers  consider  it  an  unneces- 
sary complication;  others  hold  that  with  it  economy  as  well  as 
convenience  is  gained.  A  resume  of  the  advantages  and  disad- 
vantages may  prove  interesting  especially  since  the  Government 
specifications  for  the  military  trucks  included  this  equipment. 

Many  mechanical  problems  must  be  considered  in  selecting 
electrical  equipment  for  commercial  cars.  While  these  units  have 
worked  out  satisfactorily  for  passenger  vehicles  that  are  equipped 
with  pneumatic  tires,  it  is  a  question  whether  they  will  endure 
the  greatly  aggravated  vibration  of  motor  trucks  having  solid 
tires,  stiffer  springs  and  are  compelled  to  travel  cobble-stones 
and  rough  roads.  Such  consideration  as  frequent  troubles  from 
inability  to  withstand  the  hard  usage,  are  very  important  and 
may  more  than  offset  the  advantages  gained  through  the  use  of 
such  equipment.  It  is  true  that  some  of  these  equipments  have 
worked  out  very  satisfactorily  on  commercial  cars ;  however,  they 
are  generally  designed  to  meet  these  more  exacting  conditions. 
They  are  sturdier  and  stronger  built  devices,  while  the  battery 
must  also  be  of  such  capacity  as  to  permit  frequent  starting  and 
must  have  some  special  mounting  to  resist  vibration. 

The  arguments  for  and  against  electrical  equipment,  covered 
in  the  following,  are  the  result  of  a  general  study  of  this  subject 
and  are  not  based  on  the  opinions  of  makers  of  these  units. 

Four  units  generally  comprise  the  complete  electric  system, 
the  ignition  system,  the  generator,  the  starting  motor  and  the 
battery.  Ignition  systems  were  previously  described  and  will 
not  be  considered  in  this  article.  The  generating  system  con- 
sists of  a  generator  or  dynamo,  its  drive  and  mounting  and  also 
an  output  regulator  and  reverse  current  cutout.  The  starting 
system  consists  of  an  electric  motor,  its  drive  and  mounting  and 
a  suitable  switch  for  starting  purposes.  The  link  between  the 
two  systems  is  the  storage  battery  which  serves  in  effect  as  a 
reservoir  for  accumulating  electricity. 

298 


ELECTKIC  LIGHTING  AND  8TAETING          299 

The  generators  of  different  systems  now  in  use  vary  in  con- 
struction or  type,  some  having  a  permanent  and  others  an  excited 
or  wound  field.  Fundamentally,  there  are  three  types  of  gen- 
erators in  use — shunt  wound,  compound  wound  and  differentially 
wound  generators.  The  field  itself  may  either  carry  simple  or 
compound  windings.  The  armature  revolving  between  the  poles 
of  the  field  generates  electric  current,  the  output  of  which  is 
governed  by  the  output  regulator.  The  method  of  generating  elec- 
tric current  was  described  previously  in  the  chapters  of  mag- 
netos. The  reverse  current  output  prevents  the  flow  of  current 
through  the  generator  from  the  battery. 

The  starting  motor  which  takes  the  place  of  the  ordinary  hand 
crank  is  operated  by  current  from  the  battery.  This  unit  is  sim- 
ilar but  opposite  to  the  generator  in  that  instead  of  motion  pro- 
ducing current,  current  flowing  through  the  fields  energizing 
them  and  causing  the  armature  to  rotate  produces  motion. 
Speaking  loosely,  electricity  that  has  been  pumped  into  the  bat- 
tery by  the  generator,  runs  out  through  the  motor.  If  the  motor 
is  properly  interconnected  with  the  engine  it  can  be  made  to  turn 
the  latter  over  until  it  starts. 

A  definite  amount  of  work  must  be  done  to  produce  electricity, 
and  that  work  is  done  by  the  generator.  The  electrical  energy 
that  the  generator  produces  is  stored  in  the  battery  for  use  when 
the  generator  itself  cannot  supply  the  current  as  when  the  en- 
gine is  to  be  started. 

Advantages  of  Electric  Lights  and  Starter. — The  advantages 
on  a  commercial  vehicle  of  electric  lights  and  starter  are  as  fol- 
lows in  their  order  of  importance : 

1.  Greater  economy  due  to  saving  gasoline  and  time  when 
many  stops  are  made  by  not  keeping  the  engine  running. 

2.  Increased  life  of  the  engine,  as  shutting  it  off  at  each  stop, 
eliminates  considerable  needless  wear. 

3.  Saving  of  time  over  hand  starting  increasing  the  actual 
working  hours  of  the  car  and  operator. 

4.  Better  lighting  and  easier  driving  for  night  work  and  fewer 
accidents  from  the  rear  light  going  out. 

5.  Better  finished  appearance  of  cars  for  certain  classes  of 
work. 

To  these  may  be  added  the  possibility  of  getting  more  for 
certain  types  of  cars  for  special  service,  Avhere  the  advertising 
value  is  considered. 


300    MOTOE  TRUCK  DESIGN  AND  CONSTRUCTION 

Disadvantages  of  Electric  Lights  and  Starter. — The  principal 
disadvantages  in  equipping  commercial  vehicles  with  these  units 
are: 

1.  Additional  first  cost  and  added  complications  which  the 
driver  does  not  comprehend. 

2.  Increased  maintenance  cost  and  interest  on  additional  in- 
vestment. 

3.  Decrease  in  engine  accessibility  in  making  repairs,  thus  in- 
creasing the  cost  of  these  repairs. 

4.  Unreliability  of  certain  parts,  such  as  the  storage  battery 
and  the  possibility  of  these  units  being  maintained  far  below 
their  original  efficiency. 

5.  The  effect  of  vibration  on  units  not  originally  designed  for 
commercial  car  service. 

6.  Inability  to  keep  the  battery  sufficiently  charged  owing  to 
frequent  starting  and  stopping. 

7.  Battery  and  other  electrical  troubles  aggravated  by  the 
average  commercial  car  driver  not  being  familiar  with  the  con- 
struction and  care  of  the  electrical  system. 

On  trucks  that  have  many  stops  to  make  such  as  house  to 
house  delivery,  starters  are  no  doubt  desirable,  considering  the 
high  cost  of  gasoline,  as  the  operator  will  invariably  allow  his 
engine  to  run  rather  than  crank  it  when  making  a  stop  of  a  few 
minutes.  Stopping  the  engine  will  cut  down  the  fuel  bills. 

But  whether  the  starter  will  save  time  over  cranking  seems 
to  be  disputed.  Various  arguments  are  advanced  covering  the 
point  of  economy. 

Any  type  of  delivery  car  and  even  some  of  the  large  motor 
trucks  make  more  stops  during  the  day  than  the  average  touring 
car,  and  from  the  point  of  economy  the  commercial  car  would 
seem  to  have  the  greater  need  for  a  starter.  Moreover,  the 
starter  is  also  a  convenience  and  saves  energy.  Some  imagine 
that  the  starter  will  start  the  engine  when  the  driver  cannot  start 
it.  This  is  not  true  unless  the  engine  is  too  big  to  be  spun  by 
hand.  The  average  truck  engine  can  be  spun  easily  by  the  aver- 
age driver  and  if  the  gasoline  mixture  is  getting  to  the  cylinders 
and  the  spark  is  all  right,  it  can  be  started  as  many  times  by 
man  as  by  a  self-starter.  A  self-starter  can  do  no  more  than  man, 
but  it  does  conserve  his  energy. 

Some  claim  that  the  time  saved  with  a  starter  even  when 
stops  are  numerous  is  relatively  small  compared  with  the  time 
the  operator  usually  wastes  in  other  directions.  Cold  weather 


ELECTRIC  LIGHTING  AND  STARTING          301 

must  also  be  considered,  which  may  average  four  months  per 
year,  when  it  is  really  advantageous  to  let  the  engine  idle  and 
prevent  the  radiator  from  freezing  and  to  keep  the  mixture  warm 
for  a  good  start. 

Stopping  will  increase  the  life  of  the  engine,  but  in  the  ab- 
sence of  a  starter  with  a  bonus  system  to  encourage  economy, 
the  driver  would  not  let  the  engine  run  idle  for  long.  Where, 
especially  on  the  heavy  vehicles,  the  drivers'  union  compels  the 
owner  to  provide  a  helper  on  each  car,  there  is  still  less  excuse 
to  keep  the  engine  running. 

Without  question,  electric  lights  are  preferable  to  oil  lamps, 
but  it  is  for  the  owner  to  decide,  especially  whether  they  are 
worth  their  slightly  greater  cost  if  there  is  little  operating  at 
night.  Accidents  that  may  be  traced  to  the  lighting  system  will 
be  reduced,  if  the  lighting  system  is  maintained  at  its  original 
efficiency,  which  is  doubtful  on  a  commercial  car. 

Where  appearance  is  a  large  factor,  the  additional  first  cost 
and  maintenance  are  usually  disregarded.  Under  certain  con- 
ditions, especially  on  light  deliveries,  electric  equipment  adds 
considerable  to  the  sales  value.  Conditions  here  approximate 
those  of  a  touring  car  and  there  is  no  question  of  that  feature  in 
this  case. 

Disadvantages  Discussed. — The  first  cost  of  a  commercial 
vehicle  is  what  engineers  have  been  striving  to  keep  down  and 
simplicity  aids  low  first  cost.  Electrical  equipment  will  add  a 
certain  amount  of  weight  and  expense  that  must  be  paid  by  the 
purchaser  and  as  a  motor  truck  is  purely  a  business  proposition, 
its  prime  object  being  to  carry  goods  at  the  lowest  cost,  the  starter 
must  save  time  and  money.  From  the  mechanical  viewpoint  it 
means  some  complications  that  the  average  truck  driver  does  not 
comprehend.  He  is  not  an  electrician  and  the  best  electrical 
equipment  requires  some  electrical  knowledge  at  times. 

The  question  resolves  itself  into  Avhether  starters  can  save 
enough  in  fuel  and  time  to  offset  the  increased  maintenance  cost 
and  pay  an  interest  on  the  additional  investment.  It  should 
also  be  remembered  that  this  added  equipment  will  render  the 
engine  more  inaccessible  for  repairs,  thus  adding  to  their  cost. 

There  are  certain  objections  from  a  mechanical  standpoint. 
The  battery  seems  to  be  the  weakest  unit  of  the  entire  system, 
for  this  is  subject  to  jolting  and  jarring,  which  shortens  its  life 
perceptibly  even  with  the  best  of  care.  Spring  mounting  devices 


302    MOTOE  TKUCK  DESIGN  AND  CONSTRUCTION 

may  overcome  this  difficulty,  but  a  vast  amount  of  education  is 
necessary  before  the  average  truck  driver  will  know  how  to  take 
care  of  a  storage  battery.  Even  after  this  lesson  has  been  taught, 
there  still  exists  that  human  element  which  is  responsible  for  the 
rapid  destruction  of  commercial  vehicles  through  improper  care, 
handling  and  neglect. 

Frequent  starting  and  stopping  is  another  factor  which  also 
must  be  given  consideration,  as  the  battery  must  be  of  ample 
capacity  to  provide  for  the  number  of  starts  made  during  a  day's 
work.  The  generator  must  be  of  sufficient  size  to  keep  the  bat- 
tery properly  charged  and  it  must  be  also  of  the  simplest  type. 

The  difficulty  resulting  from  the  driver's  lack  of  knowledge 
will  probably  diminish  as  use  of  the  system  becomes  more  uni- 
versal. 

Opinions  of  engineers  differ  as  to  the  final  solution  of  the 
problem.  At  present  the  question  of  electrical  equipment  seems 
to  be  up  to  the  public,  as  the  personal  view  of  the  purchaser  ap- 
pears to  be  the  greatest  factor.  All  makers  supplying  electric 
units  as  regular  equipment  will  omit  these  if  requested  to  do  so. 
Makers,  who  do  not  regularly  equip  their  vehicles  with  these 
units,  will  supply  them,  if  the  OAvner  will  pay  the  difference. 

The  battery  seems  to  be  the  troublesome  unit  and  the  weakest 
point  of  the  entire  system.  So  far  as  the  lighting  is  concerned 
the  problem  may  be  solved  by  sending  current  directly  from  the 
generator  to  the  lamps,  similar  to  the  Ford  car,  but  without  its 
irregular  lighting  characteristics.  The  starter  problem  is  more 
aggravated,  but  may  be  solved  in  some  as  yet  unfound,  but 
equally  simple,  way. 


MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION     303 


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304    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION     305 


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306    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


MOTOE  TRUCK  DESIGN  AND  CONSTRUCTION    307 


308    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION    309 


310    MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION 


MOTOR  TRUCK  DESIGN  AND  CONSTRUCTION     311 


A 


INDEX 


Advantages   and   disadvantages 

of  two  and  four  cycle  motors 

Advantages   of   locating  motor 

under  hood   

Advantages    of    various    motor 

lubricating  systems    

Air  cooling   

Cushion  radiator  mounting 

Automatic  spark  control 

Axle,  Bevel-gear  type    

Chain-driven    

Double  reduction  type 

Front   bearings    

Built-up  type 

Cast  type 

Construction  of   

Drop-forged  type 

Frame  attachment  of. 

General  types  of   

Double  reduction  type  of.  . 

Internal  gear  type   

Rear  types  of 

Shaft-driven  types    

Worm-gear  type  of    

Semi-floating  type  of 
Three  quarter  floating  type 

of 

Full  floating  type  of   


Bevel-gear  axle    

Brake,   adjustments    

Band    type     

Concentric  type 

Control,  lubrication  of 

Equalizers    

Hydraulic  type    

Internal  and  external  . 

Jackshaf t   type    

Linkage    

Location  of   

Method  of  application 


Page  Page 

Brake,  on  shaft-drive  models  . .  176 

Rear  wheel   175 

^Q               Sauer  Motor   181 

Shoe   type    176 

2               Timken  duplex 180 

Types   of    172 

38 

39  C 

46       Carburetion     50 

65       Carburetor,  Construction  of   . .  51 

140               Dash    adjustment    53 

135               Float,  function  of 51 

143               Mounting    58 

191               Throttle    52 

190               Troubles    57 

184               Types    52 

184       Cellular  type  radiator  core   ...  41 

186       Centrifugal  type  water  pump.  .  47 
184       Center    bearing    for    propeller 

183                   shafts    122 

143               Control  and  pedal  mounting  260 

145       Chain    drive    132 

154               Driven  axle 135 

142               Drive,  advantages  of 140 

151               Driven  front  wheel  drive..  163 

154                        Jack  shaft 133 

Characteristics  of  two-cycle  en- 

154           gines    6 

154       Chassis,   definition   of    1 

Types,  advantages  and  dis- 
advantages   of    3 

140       Circuit  Breaker,  the    63 

182       Clutch,  band  type 102 

177  Comparisons  of   102 

179               Gone   types    96 

264               Dry  Plate  type    •• 10° 

263               Location  of 95 

174               Multiple  disc  type 98 

178  Necessity  of   95 

173       Coil    ignition    68 

262               Non-vibrating    72 

172               Transformer,   type   of 68 

172       Compression  release 26 

313 


314 


INDEX 


Page 

Condenser    64 

Connecting-  rod,  construction  of  15 

Function  of 16 

Control,  brake,  clutch  and  gear  255 

Conventional  type 253 

Locations  and  their  advan- 
tages      254 

Mounting-  of    260 

Progression  type  of 261 

Sliding  shaft  type    256 

Spark  and  throttle          ....  255 

Swinging  lever  typfe 258 

Conversion  of  reciprocating  mo- 
tion into  rotary  motion   ....  16 

Crank  case,  the   21 

Construction  of   21 

Function   of    21 

Crank  shaft,  construction  of  .  .  15 

Cylinder,    construction   of    ....  14 

Combination  type   19 

Grouping  of    20 

Cylinder,  L-head  type    18 

T-head  type 18 

Types  of 17 

Valve-in-head  type    18 

Material  of   14 

Cross  steering    208 


Differential,  function  of 125 

Operation  of 127 

Bevel  gear  type   126 

Spur  gear  type    127 

Lock    128 

Worm  gear  type   129 

Semi-locking  type   129 

Semi-locking    type,    opera- 
tion of    130 

Difficulty  of  transmitting  power  114 

Distributor,   ignition    65 

Disadvantages  of  locating  mo- 
tor under  hood    3 

Double  reduction  axle   .  .  .  . 143 

Drag  link,   location   of 198 

Lay  out  of    198 

Proportions  of  201 

Types  of  209 

Dual  ignition  systems 67 


Page 
E 

Electrically  equipped  trucks, 
advantages  and  disadvan- 
tages of  298 

Electric  lights  and  starter,  ad- 
vantages of   ....   299 
disadvantages  of .  .   300 
discussion     of     ad- 
vantages     301 

Electric-driven  four-wheel  drives  171 
Electromotive      force,      propor- 
tions  of    79 

Enclosed  chain  drive 140 

Engine    construction    14 


Fan    48 

Location  of   48 

Final  drive,  definition  of   132 

Flywheel,  function  of    17 

Float  chamber  of  carburetor.  .      51 
Four-cycle  engine  operation   . .        8 
Four-cylinder     engine,     advan- 
tages and  disadvantages  of.  .      10 

Four-wheel   drive    166 

Combined     chain 

and  shaft 171 

Electric     type      of 

drive    171 

Frame,   function  of    210 

Frame,  Trend  of  design 218 

Pressed  steel,  advantages  of  211 

Cross  members    211 

Rigid    type 212 

Rigid  type  effect  of 212 

Flexible    213 

Frame,  pressed  steel,  construc- 
tion   of     214 

Structural  channel  type   . .   217 
Structural  I-beam  type  ...   218 

Tractor   type    217 

Friction,  definition  of    30 

Front    and    four-wheel    drives, 

advantages  of 162 

Front  wheel,  throw  off    192 

Function  of  cam  shaft 20 

Of  crank  shaft,  piston  and 
connecting  rod 16 


INDEX 


315 


Page 

Function  of  motor  lubricating 
system 29 


Gasoline  tank,  mounting  of    . .   246 

Construction  of 244 

Bolster  type    246 

Pressed  steel  type  ....   248 
Feed,    pressure   system  251 
Systems,       advantages 
and  disadvantages  of  252 

Gear  type  water  pump 47 

Gear-driven  front  wheel  drive.    166 

Governor,   Definition   of    85 

Defects    86 

Operation     86 

Centrifugal  type    88 

Hydraulic   type    89 

Automatic  type    89 

Advantages    and    disadvan- 
tages of   94 

Gravity,  feed  fuel  system    245 


Heating  fuel  mixture    57 

High  Tension  Jump  spark  igni- 
tion      60 

Hollow  propeller  shaft   122 

Honeycomb  radiator  core    41 

Hotchkiss  drive   156 

Spring  mounting  for  .  .  239 

Hydraulic  type  governor    86 


Ignition,  systems   of    76 

Coil    68 

Low     tension     make      and 

break    59 

Timer    75 

Independent     ignition     system, 

summary  of    67 

Inductor  magneto 77 

Operation    of    79 

High  tension  type  ....  81 

Shaft  78 

Induction  of  electrical  impulses  62 

Internal  gear  axle   145 


Page 
J 

Jack  shaft,  chain  drive    132 

Jump  spark,  low  tension 59 

High  tension   60 


Kick  switch 69 

Knuckle  lever,  angles  of 194 

Location  of   .  .    195 


Lack  of  accessability    4 

Lay   out   of  chassis    1 

Live  axle  drives 168 

Locating  motor  under  seat  op- 
posite hood   5 

Motor  under  seat    4 

Low  tension  jump  spark  igni- 
tion      59 

Magneto,    construction 

of    70 

Make    and   break   igni- 
tion      59 

Magneto  wiring 70 

Lubricants    31 

Requirements  of    30 

Lubrication  splash  system 31 

Circulating    splash    system  33 

Gravity  feed   34 

Force    feed    35 

M 

Magneto,  classification  of    ....  60 
And    battery    systems    low 

tension    69 

High  tension    61 

Low  tension    69 

Magnetic  lines  of  force    61 

Mechanical  oilers    32 

Methods  of  transmitting  power  132 

Mixing  chamber    51 

Motor  cooling  system    39 

Lubrication   29 

Methods  of    31 

Speed,   method   of   control- 
ling      85 

Muffler  cutout 266 

Construction    of    265 


316 


INDEX 


Page 
Muffler  cutout,  function  of  ....   265 

Location  of 265 

Types   of    266 

Multiple   cylinder  engines    ....      12 
Multiple   feed   oiler    32 


Oil  pump  gear  type 32 

Plunger  type  32 

Operation  of  fan  48 

Two-cycle  gasoline  motor . .  6 

Four-cycle  gasoline  motor.  8 


Pin  type  of  universal  joint  ....  118 

Piston  construction  of 15 

Poppett  valves   17 

Power  losses  in  engine 4 

Power  plant  arrangement 2 

Mountings',    description.  320 

Rigid  type 221 

Three  point  type. .  221 
Three    point    main 

frame  type    ....  222 

Floating  type   225 

Sub-frame  type    226 

Principle   of    self   induction    .  .  73 

Propeller  shaft    122 

Brake    176 

Mountings  of    122 

Tubular 122 

Solid    122 

Divided   123 

Slip    joint    120 

Pumps,  oil 32 

Water    46 

Push  rod   adjustment    21 

Function    of    .  21 


Radiator,  construction  of  ....  41 

Built-up  type  42 

Mountings  44 

Rebound  clips 239 

Rubber,  crude  282 

Wild 282 

Cultivated  283 

Manufacturing  process  of.  283 

Rims    .  .   284 


Page 
S 

Safety    spark    gap 66 

Seat,    location    of 1 

Solderless  Radiator    43 

Spark,   fixed    65 

Variable    63 

Spring,   auxiliary    235 

Alignment    241 

'Clips    241 

Full   elliptic  type 234 

Lubrication,    of    242 

Mountings   of    236 

Overload    241 

Rebound   clips    239 

Spring   Shackles    239 

Semi-Elliptic   type    231 

True  sweep  type 231 

Double  sweep  type. . . .   233 

Types    of    230 

Three  quarter  platform 

type     235 

Stewart   vacuum   feed 250 

Steering  gear  bevel  pinion  type  203 

Irreversible  type   196 

Principle   of    200 

Ratios    of    197 

Rack  and  pinion  type 202 

Reversibility    of     196 

Screw  and  nut   type 206 

Wheel  and  Mast 200 

Worm  and  sector 203 

Worm   and  wheel 205 

Steering    mechanism,     descrip- 
tion of 192 

Switch,   function   of 66 

Operation    of    69 


Tie    rod    201 

Location   of   197 

Timer,   ignition    75 

Tire,   care   of    289 

Contour    and    construction 
of   285 

Demountable   type    286 

Tire   development    280 

Effect   of   speeding 291 

Rough    roads    292 


INDEX 


317 


Page 

Tire,  effect  of  wheel  alignment  292 
Anti-skid   devices    ....   294 

Neglected    cuts    294 

Skidding    and    applica- 
tion of  brakes 295 

Running  in  car  tracks  295 

Oils,   grease,   etc 296 

Tire,  hard  rubber  base  type..   284 

Metal   base   type 282 

Solid    truck    type 284 

Pressed   on   type 288 

Torque,   definition   of 103 

And  propulsion,  method  of 

providing  for    155 

Transmission,    types    of 104 

Friction   type    104 

Planitary  type    104 

Sliding  gear  type   106 

Progressive    sliding   type...  107 

Selective  sliding  type    108 

Positive  clutch  type    Ill 

Automatic  engagement  type  113 
Mounting  flexible  type   ...   228 
Transforming  low  tension  into 

high  tension  current 63 

Types    of   chasses 3 

Of      cylinders      and      their 

parts    13 

Of    front   wheel   drives 162 

Of    springs    230 

Of  two-cycle  engines 6 

Two-cycle  engine,  advantages 
and  disadvanta- 
ges of  10 

Characteristics    of.       6 
Two-cylinder    opposed   motor.  .      28 

U 

Unit    power    plant    22 

Flexible    mounting 

of    210 

Universal  joint,  block  and  trun- 
nion  type    116 


Page 

Universal  joint,  cross  type  ....  115 

Fabric   type    121 

Internal  gear  type. ...  115 

Pin   type    118 

Split  ring  type 115 

Necessity  of   114 


Valve,  construction  of 17 

Function   of    17 

Location    of    17 

Mechanism     for     L    head 

motor    23 

Valve     in     head 

motor    24 

Overhead   valve 

motor    24 

Operation    of    20 

Spring,   function   of 20 

Vane  type  water  pump 10 

Vaporization  of  fuel 50 

Variable  spark  control 83 

Vehicle  springs 230 

Vertical  tube  type   of  radiator 

core    74 

Vibrator,  action  of 74 

W 

Water  cooling    40 

Pump,    types    of 46 

Wheel,  advantages  of  steel 273 

Advantages    and    disadvan- 
tages of    278 

Cast   steel   type 272 

Construction  of  cast  steel.  274 

Dual  type  of    274 

Double  disc  type  of  steel.  .  276 

Spindle  inclination,  of 195 

Single  disc,  type  of  steel.  .  275 

Spoke  type  of  cast  wheel.  276 

Wood    artillery   type 272 

Worm-drive    axle    151 


318  INDEX 

ATPENDIX. 
LIST  OF  PLATES. 

Page  Page 

Fagoel  heavy  duty  chassis.  .  .  .  311       Schackt    worm-drive    chassis.  .   310 

Federal   3^-ton   chassis 312       Stewart  3J-ton  chassis 305 

Kissell  general  delivery  trucks.  309       United      stages      worm-drive 

Military   class   B   chassis 303  chassis    304 

Muskegon,  2-ton  chassis 308       White  heavy  duty  chassis 307 

Packard     5-ton     worm-drive 

chassis    306 


MOTOR  VEHICLES 
AND  THEIR  ENGINES 

A  practical  handbook  on  their  care, 
repair,  upkeep  and  management 

By  EDWARD  S.  FRASER 

American  Bosch  Magneto  Corporation;    Formerly,  Captain  C.  A..  U-  S.  A.,  Instructor  Motor 
Transportation  Course,  Coast  Artillery  School 

and  RALPH  B.  JONES 

Willys  Overland  Company;    Formerly,  Captain  C.  A.,  U.  S.  A.,  Instructor  Motor  Transporta- 
tion Course,  Coast  Artillery  School 


A  complete  book  on  the  auto- 
mobile written  in  the  simplest 
language  and  with  technicalities 
reduced  to  a  minimum. 

The  fundamentals  of  gas  motor 
operation,  as  well  as  the  care  and 
operation  of  the  principal  acces- 
sories of  motor  vehicles  are  dis- 
cussed in  detail  and  at  greater 
length  than  usual. 

The  last  four  chapters  are  the 
result  of  the  authors'  observations 
and  experience  with  the  great 
number  of  trucks,  tractors,  auto- 
mobiles and  motorcycles  operat- 
ing under  their  supervision,  and 
a  study  of  them  will  be  of  great 
help  in  obtaining  the  maximum 
economy,  efficiency  and  life  of 
the  apparatus. 


CONTENTS 

THE;  GAS  ENGINE 
PRINCIPLES  OF  TWO  AND  FOUR-CYCLE 

ENGINES 

TIMING 

ENGINE  BALANCE  AND  FIRING  ORDER 

COOLING  SYSTEMS 
FUEL  FEED  SYSTEMS 

FUELS 
ELEMENTS  OF  CARBURETION 

CARBURETORS 
PUDDLE  TYPE  CARBURETORS 

MAGNETISM 

ELEMENTARY  ELECTRICITY 
BATTERIES 
INDUCTION 

BATTERY  IGNITION  SYSTEMS 
MAGNETOS:    ARMATURE  TYPE 

MAGNETOS:    ROTOR  TYPE 

DUAL  AND  DUPLEX  IGNITION  SYSTEMS 

STARTING  AND  LIGHTING   SYSTEMS 

POWER  TRANSMISSION 

CLUTCHES 
TRANSMISSIONS 

DRIVES 

DIFFERENTIALS 
RUNNING  GEAR 
TIRES  AND  RIMS 
HOW  TO  DRIVE 
ENGINE  TROUBLES  EXPERIENCED  ON 

THE  ROAD 

LUBRICATION 

CARE  AND  ADJUSTMENT 

CARE  AND  ADJUSTMENT  TABLES 


350  pages,  6x9  inches,  Flexible  Fabrikoid,  postpaid  $2.00 
278  pictures,  many  in  colors 


D.  VAN  NOSTRAND    CO.,  Publishers 

25  PARK  PLACE  NEW   YORK 


THE  LITERATURE  OF  THE 

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